LIBRARY 


UNIVERSITY  OF  CALIFORNIA, 


UBRARY 
G 


Class 


OUTLINES  OF 
PHYSIOLOGICAL  CHEMISTRY 


OUTLINES  OF 


PHYSIOLOGICAL  CHEMISTRY 


BY 


s.  P.|BEEBE,  PH.D. 

Physiological  Chemist  to  the  Huntington  Fund  for  Cancer  Research 


AND 


B.  H.  BUXTON,  M.D. 

Professor  of  Experimental  Pathology,  Cornell  Medical  College 


Neto  ¥otfc 

THE  MACMILLAN  COMPANY 

LONDON:    MACMILLAN  &  CO.,  LTD. 

1904 


T 


BIOLOGY 

LIBRARY 

G 


BENEBAL 


COPYRIGHT  1904 
BY  THE  MACMILLAN  COMPANY 


PRESS  or 

?HI  NEW  ERA  PRINTING  COMPAWV. 
LANCASTER,  PA. 


PREFACE. 

THE  subject  of  physiological  chemistry  is  becoming  of  greater 
importance  every  day,  but  so  far  as  we  are  aware  there  is  no 
book  of  small  compass  which  attempts  to  deal  with  the  theoret- 
ical side  of  the  many  questions  involved.  There  are  plenty  of 
laboratory  guides  but  in  order  to  grasp  the  significance  of  his 
laboratory  work  the  student  has  to  pick  up  most  of  his  ideas  from 
books  which  deal  primarily  with  subjects  of  purely  chemical  in- 
terest, and  only  secondarily  with  those  of  special  importance  to 
the  physiologist. 

We  have  endeavored  to  go  straight  to  the  point,  dealing  only 
with  questions  bearing  directly  on  physiological  problems. 

In  order  to  keep  the  book  within  reasonable  bounds  it  has 
been  found  necessary  to  assume  for  the  reader  some  knowledge 
of  inorganic  chemistry,  and  for  the  same  reason  it  is  impossible 
to  avoid  making  some  general  statements  which  would  have  to 
be  qualified  or  modified  to  some  extent  if  taken  up  in  detail. 
It  is  sincerely  hoped,  however,  that  no  actual  errors  have  been 
committed.  Since  this  is  not  intended  for  a  laboratory  guide, 
sufficient  details  for  applying  various  tests  have  not  been  given 
in  most  cases.  The  object  has  simply  been  to  explain  the 
nature  of  the  reactions. 

LOOMIS  LABORATORY,  NEW  YORK, 
April,  1904. 


CONTENTS. 


CHAPTER  I. 

PAGE. 

THEORY  OF  SOLUTIONS.    IONIZATION.     .        .        .  1 

CHAPTER  II. 

ORGANIC  CHEMISTRY  OR  THE  CHEMISTRY  OF  CARBON  COM- 
POUNDS   22 

CHAPTER  HI. 

COMBINATIONS  OF  THE  OXIDATION   PRODUCTS  OF  THE  PAR- 
AFFINS WITH  EACH  OTHER 36 

CHAPTER  IV. 

HALOGEN  AND  NITROGEN    DERIVATIVES  OF  CARBON  COM- 
POUNDS   54 

CHAPTER  V. 
CYCLIC  COMPOUNDS 73 

CHAPTER  VI. 
THE  PROTEIDS 99 

CHAPTER  VH. 
ENZYMES 0        .  160 

CHAPTER  VIH. 
DISEASE  AND  IMMUNITY  ...  -175 


Vll 


OUTLINES  OF  PHYSIOLOGICAL  CHEMISTRY. 


CHAPTER  I. 

THEORY  OF  SOLUTIONS.     IONIZATION. 

THE  researches  of  the  last  fifteen  years  have  made  plainer 
the  mechanism  of  reactions  taking  place  in  solution.  Practi- 
cally all  of  the  reactions  that  are  of  interest  to  the  physiological 
chemist  take  place  in  solution,  so  that  it  is  important  to  know 
something  about  the  new  chemistry. 

DISSOCIATION. 

When  acids,  bases  and  salts  are  dissolved  in  water  they  are 
said  to  dissociate,  i.  e.y  the  molecules  to  a  certain  extent  break 
apart.  These  fragments  carry  a  charge  of  electricity  and  are 
called  ions.  Thus  in  a  10  per  cent,  solution  of  sodium  chloride 
(NaCl)  we  have  H2O  +  NaCl  +  Na+  -f  C1-.  Some  of  the  salt 
exists  in  the  molecular  (Na  —  Cl)  condition,  the  remainder 
being  ionized.  The  metal  carries  the  positive  charge  and  is 
called  the  cation  (icara,  down)  ;  the  acid  (Cl)  carries  the  negative 
charge  and  is  called  the  anion  (ava,  up). 

In  an  ordinary  solution  the  electrically  charged  cations  and 
anions  are  equally  distributed  throughout,  but  on  passing  an 
electric  current  through  the  solution,  the  cations  fly  to  the 
cathode  or  negative  ~  pole,  and  the  anions  to  the  anode  or  posi- 
tive +  pole. 

Diagrammatically  : 


-f 

Pole  Pole 


2  OUTLINES   OF  PHYSIOLOGICAL  CHEMISTRY. 

Acids,  bases  and  salts  dissociate  and  are  called  electrolytes. 
Other  substances  do  not  dissociate  —  non-electrolytes.  Water 
(H2O)  does  not  dissociate  and  of  itself  is  a  non-conductor.  An 
electric  current  passed  through  water  is  carried  solely  by  the 
ions  in  solution. 

The  Na+  ion  must  not  be  confused  with  the  Na  atom.  The 
ion  is  the  atom  plus  the  charge  of  electricity  which  causes  it  to 
behave  very  differently. 

The  ions  are  continually  moving  about  in  the  solution  and 
whenever  a  Na+  ion  comes  in  contact  with  a  Cl~  ion  they  com- 
bine to  form  for  an  instant  a  molecule  of  undissociated  sodium 
chloride  (Na  —  Cl),  which,  however,  immediately  dissociates 
again.  It  is  obvious  that  the  more  concentrated  the  solution 
the  oftener  do  the  ions  come  in  contact  and  consequently  the 
smaller  is  the  percentage  of  dissociation.  A  very  dilute  solu- 
tion of  most  acids,  bases  or  salts  is  completely  dissociated. 

The  dissociation  may  be  measured  by : 

1.  Measuring  the  elevation  of  the  boiling  point  of  water 
caused  by  dissolving  a  known  amount  of  salt  in   a   known 
amount  of  water. 

2.  Measuring   the  depression  of  the  freezing   point  under 
the  same  conditions. 

3.  Measuring  the  electrical  conductivity  of  the  solution. 
Explanations.  —  1  and  2.  If  one  molecule  of  any  substance 

is  dissolved  in  one  hundred  molecules  of  any  liquid  of  a  dif- 
ferent nature  the  lowering  of  the  freezing  point  or  the  raising 
of  the  boiling  point  of  this  liquid  is  always  the  same  or  very 
nearly  so.  When  acids,  bases  or  salts  are  dissolved  in  water 
the  depression  of  the  freezing  point  is  much  greater  than  it 
should  be  according  to  the  above  law  of  Raoult.  With  dilute 
hydrochloric  acid  the  depression  is  nearly  twice  the  normal ; 
with  barium  chloride  three  times  the  normal. 


THEOEY   OF   SOLUTIONS.  3 

Hydrochloric  acid  gives  two  ions  and  barium  chloride  three, 
the  ion  lowering  the  freezing  point  to  the  same  extent  as  a 
molecule. 

For  the  same  reason  the  boiling  point  is  raised. 

3.  Water  is  not  dissociable  and  the  conductivity  depends  on 
the  degree  of  ionization. 

Reactions  in  solutions  are  reactions  between  ions. 

Old  method 

Ha  +  NaOH  =  H2O  +  NaCl 
New  method 


leaving  Na  and  Cl  ions  in  solution.  The  reaction  takes  place 
because  when  the  hydrogen  (H+)  ions  come  in  contact  with  the 
hydroxyl  (OH~)  ions,  water  (H2O)  is  formed  which  is  not  dis- 
sociated, and  so  the  ions  (OH~  and  H+)  are  removed  from  the 
sphere  of  action.  The  neutralization  of  any  acid  by  any  base 
is  due  to  the  same  cause. 

AgNOs  +  NaCl  =  AgCl  +  NaNO8 
or 

Na+  +[^+Ag1-fNO;>  AgCl. 

There  is  reaction  because  AgCl  is  insoluble  in  water  and  as  fast 
as  Ag  and  Cl  ions  come  in  contact  they  are  removed  from 
solution. 

In  potassium  chlorate,  KC1O3,  there  is  a  large  amount  of 
chlorine  but  there  is  no  Cl~  ion.  K+  +  C1O~  is  the  condition 
in  solution. 

Chloroform,  CHCl^  contains  much  more  chlorine  than  NaCl, 
but  chloroform  does  not  dissociate  and  consequently  it  does  not 
show  a  reaction  with  silver  nitrate. 

Another  example  may  be  given. 


4  OUTLINES    OF    PHYSIOLOGICAL   CHEMISTRY. 

Sulphuric  acid  (H2SO4)  added  to  a  solution  of  barium  chloride 

(BaCl2) 

I  +  2C1-    BaSO4. 


In  this  case  as  fast  as  the  barium  ions  are  neutralized  by  the 
sulphate  ions,  insoluble  BaSO4  is  formed  which  does  not  dis- 
sociate and  consequently  the  barium  and  sulphate  ions  are 
gradually  removed  from  the  solution. 

DISSOCIATION  OF  ACIDS  AND  BASES. 

1.  Acids  yield  H+  hydrogen  ions. 

2.  Bases  yield  OH~  hydroxyl  ions. 

1.  Acids  are  substances  which  give  a  hydrogen  ion  when 
dissociated. 
Examples : 

H+  -f  Cl-        Hydrochloric  acid. 

H+  +  NO-     Nitric  acid. 

It  was  formerly  supposed  that  acid  properties  were  due  en- 
tirely to  the  presence  of  oxygen.  The  word  means  "acid 
former."  We  now  know  that  the  cause  of  acidity  is  the  hy- 
drogen ion.  The  strength  of  an  acid  depends  entirely  upon  the 
number  of  hydrogen  ions  present  in  a  solution  of  it,  L  e.,  upon 
the  extent  to  which  the  acid  is  dissociated. 

Taking  the  sulphur  acids  : 

H2S  Hydrosulphuric. 
H2SO3  Sulphurous  acid. 
H2SO4  Sulphuric  acid. 

We  know  very  well  that  the  one  containing  the  most  oxygen 
is  the  strongest  acid,  i.  e.,  the  introduction  of  oxygen  facilitates 
the  dissociation  of  H  from  the  molecule. 


THEORY   OF   BOLUTIONS.  5 

On  the  other  hand  with  the  acids  of  phosphorus 

H3PO2     Hypophosphorous  acid, 
H3PO3     Phosphorous  acid, 
H3PO4     Phosphoric  acid, 

the  introduction  of  oxygen  decreases  acidity,  i.  e.,  phosphoric 
acid  is  less  dissociated  than  hypophosphorous  acid.  In  a 
majority  of  cases  the  introduction  of  oxygen  facilitates  dissocia- 
tion and  therefore  increases  acidity  but  the  rule  does  not  always 
hold  good. 

NOMENCLATURE  OF  Acros. 

The  method  of  naming  inorganic  acids  is  intended  to  show 
the  oxygen  relations  and  was  adopted  when  the  acid  properties 
were  supposed  to  depend  upon  the  oxygen  content. 

Example.  Acids  of  Chlorine.  Acids  containing  no  oxygen 
have  the  prefix  hydro. 

HC1  Hydrochloric. 

HC1O  Hypochlorous. 

HC1O2  Chlorous. 

HC103  Chloric. 

HC1O4  Perchloric. 

From  these  acids  the  following  potassium  salts  may  be 
formed. 

KC1  Potassium  %oVochloride  commonly  called  chloride. 

KC1O  Potassium  fo/pochlorite. 

KC1O2  Potassium  chlorite. 

KC1O3  Potassium  chlorate. 

KC1O4  Potassium  perchlorate. 

Acids  ending  in  ic  form  salts  ending  in  ate. 
Acids  ending  in  ous  form  salts  ending  in  ite. 


6  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTEY. 

2.  Bases  are  substances  which  yield  hydroxyl  (OH)  ions  on 
dissociation.  The  greater  the  number  of  hydroxyl  ions  the 
stronger  the  base. 

The  hydroxides  of  the  alkali  metals  potassium,  sodium, 
lithium,  being  very  soluble,  dissociate  readily  and  are  the 
strongest  bases.  The  hydroxides  of  the  alkaline  earths, 
barium,  calcium,  strontium,  dissociate  less  readily,  so  are  some- 
what weaker  bases. 

The  hydroxides  of  the  heavy  metals  are  but  slightly  soluble, 
so  are  very  much  weaker.  Some  of  them,  like  aluminic 
hydroxide,  dissociate  in  the  presence  of  a  strong  acid,  yielding 
hydroxyl  ions,  whilst  in  the  presence  of  a  strong  base  they 
yield  hydrogen  ions.  Thus  under  different  conditions  they  act 
either  as  acids  or  bases,  the  action  being  due  to  the  character 
of  their  environment.  We  may  have  potassium  aluminate  or 
aluminum  sulphate. 

Example  of  the  formation  of  a  salt 

KOH  +  HNO8  =  KNO3  +  H2O 

K+     cnr       +  ™3        o  +  K+ 


The  latter  forming  the  molecule  KNO3  on  concentration  of 
the  solution.  In  representing  by  equation  the  reaction  between 
an  acid  and  a  base  it  is  therefore  always  : 


K  iOH  -f  H|  ON02  =  K  —  O  —  NO2  +  H2O 
not 

KO  !  H  +"HO  j  NO,  =  K  -  O  -  NO,  +  H2O 


Potassium  nitrate,  not  nitrate  of  potash. 

The  above  gives  a  general  idea  of  the  mechanism  of  reactions 
between  inorganic  compounds  taking  place  in  aqueous  solution, 
and  the  same  applies  also  to  a  great  extent  to  organic  com- 
pounds. But  there  are  a  large  number  of  reactions  which  take 


THEORY    OF   SOLUTIONS.  7 

place  without  dissociation  and  it  is  not  necessary  to  refer  all  of 
them  to  the  action  of  +  and  ~  ions.  Chemical  activity  does 
not  necessarily  depend  upon  ions. 

CHEMICAL  EQUILIBRIUM. 
1.  Equilibrium  of  Reactions. 

When  two  substances  which  react  chemically  are  brought 
together  in  the  same  solution  the  reaction  begins  at  once  with  a 
certain  velocity,  which  depends  upon  the  temperature  of  the 
solution  and  its  concentration.  As  the  reaction  proceeds  its 
speed  gradually  decreases  until  the  products  of  the  action  have 
attained  a  definite  concentration.  This  is  a  condition  of  equi- 
librium and  no  matter  how  long  the  substances  are  left  in  the 
solution  there  is  no  further  change  in  the  concentration. 

This  is  generally  illustrated  by  the  action  of  acetic  acid  upon 
alcohol. 

Alcohol  -f  acetic  acid  =  acetic  ester  -4-  water. 

The  acid  begins  to  act  upon  the  alcohol  at  once  and  as  it  is 
gradually  used  up  the  amount  of  ester  formed  in  a  unit  of  time 
decreases  until  finally  we  have  a  condition  where  the  alcohol 
and  acid  do  not  further  decrease,  and  the  ester  and  water  do  not 
increase. 

This  is  a  condition  of  equilibrium.  There  is  still  some  free 
acid  and  some  free  alcohol  and  these  two  substances  continue  to 
react  on  one  another,  yet  the  amount  of  each  in  the  solution 
does  not  decrease.  This  is  explained  by  the  fact  that  this 
reaction,  like  chemical  reactions  in  general,  is  a  reversible  one. 

Reversion. — When  acetic  ester  is  added  to  water  it  reacts  with 
the  latter  to  form  alcohol  and  acetic  acid.  A  simple  way  of 
writing  the  reaction  is  : 

Alcohol  -f  acetic  acid  *  ^  acetic  ester  -f  water. 


8 


OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 


The  double  arrows  indicate  that  the  reaction  may  proceed  in 
either  direction. 

In  the  first  reaction  described,  as  soon  as  some  ester  is  formed 
it  begins  to  react  with  the  water  to  form  alcohol  and  acetic 
acid,  i.  e.,  to  reverse  the  action.  The  velocity  of  the  reverse 
action  is  slow  at  first  because  the  concentration  of  the  ester  is 
small,  but  it  increases  with  the  latter  until  finally  the  amount 
of  ester  formed  in  a  unit  of  time  is  equal  to  the  amount  decom- 
posed. The  condition  of  equilibrium  is  then  the  condition 
when  the  velocities  in  the  two  opposite  reactions  are  equal. 

There  is  a  condition  of  equilibrium  for  every  reaction,  but  in 
some  cases  the  action  in  one  direction  is  so  enormously  stronger 
than  the  action  in  the  other  direction,  that  the  former  is  able  to 
push  the  latter  over  almost  to  a  vanishing  point,  and  conse- 
quently the  reaction  may  appear  to  be  practically  complete. 

The  point  of  equilibrium  may  be  given  diagrammatically  for 
three  imaginary  different  reactions.  The  length  of  the  arrows 
indicates  the  vigor  in  each  direction. 


505 
a- 


5QJ? 


75* 
a 


E 


E  point  of  equilibrium. 

This  method  of  considering  chemical  reactions  is  of  great 
value  to  the  physiological  chemist,  and  may  be  approached  from 
another  point  of  view. 

2.  Equilibrium  of  Solutions. 

Suppose  we  make  what  is  called  a  saturated  solution  of 
sodium  chloride.  The  conditions  are  as  follows  : 


NaCl 

Solid. 
1 


NaCl 

In  solution. 
2 


Ionized. 


THEORY   OP   SOLUTIONS. 


9 


When  a  solution  is  saturated  as  much  solid  dissolves  as  pre- 
cipitates out  in  a  given  time.  There  is  therefore  equilibrium 
between  1  and  2.  There  is  also  equilibrium  between  2  and  3 
when  the  amount  which  dissociates  equals  the  amount  returning 
to  the  undissociated  condition.  There  are  here  two  opposing  ac- 
tions. Some  of  the  molecules  of  salt  are  breaking  apart  into  ions, 
whilst  some  of  the  ions  are  combining  to  form  molecules  of  salt. 

If  we  now  pass  into  this  satu- 
rated solution  some  gaseous  hydro- 
chloric acid,  some  of  it  dissolves  and 
dissociates.  We  thereby  increase 
the  number  of  Cl  ions. 

HC1  ^  H+  +  C1-. 

Since  now  the  Na+  ions  come  in 
contact  with  Cl~  ions  more  often 
than  they  previously  did,  the  com- 
bining action  will  exceed  the  disso- 
ciation for  a  time,  and  more  salt 
will  pass  into  the  undissociated  con- 
dition. But  the  solution  is  already 
saturated  with  undissociated  salt,  so 
that  some  must  precipitate  out  in 
solid  form  and  this  precipitation  will 
continue  until  a  new  plane  of  equili- 
brium is  established. 

Suppose  we  have  the  conditions  represented  in  the  drawing. 
A  solution  saturated  with  both  hydrochloric  acid  and  sodium 
chloride  and  arranged  so  that  pressure  can  be  produced  upon 
the  gaseous  HC1  above  the  solution.  The  conditions  of  equi- 
librium may  be  thus  represented  : 

Na++cr+cr+H+ 


Gaseous 
HCl 


FIG.  1. 


NaCl  » 
Solid 
undissolved. 


S  XaC1 

In  solution 
undissociated. 


Ions. 


In  solution     Gas  above 
undissociated.    liquid. 


10  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

There  is  complete  equilibrium. 

1.  As  much  salt  dissolves  in  a  unit  of  time  as  precipitates 
from  solution. 

2.  As  much  salt  dissociates  into  ions  in  a  unit  of  time  as  is 
formed  by  recombination  of  ions. 

3.  As  many  HC1  molecules  fly  off  from  the  surface  of  the 
liquid  in  a  unit  of  time  as  there  are  molecules  entering  the 
liquid  from  the  gas. 

We  now  bring  the  piston  down,  thereby  increasing  the  pres- 
sure on  the  HC1  gas.  This  causes  more  gas  to  dissolve,  which 
in  turn  increases  the  number  of  H  and  Cl  ions.  The  increase 
in  Cl  ions  causes  an  increased  formation  of  undissociated  sodium 
chloride  which  in  turn  causes  a  separation  of  a  small  amount  of 
solid  salt  from  the  solution. 

"We  might  cause  further  changes  by  altering  the  temperature. 

There  is  everywhere  a  continual  striving  for  equilibrium 
which  causes  chemical  changes  and  physical  changes  as  well. 
The  factors  concerned  in  the  equilibrium  of  living  matter  are  so 
numerous  and  complex  that  very  slight  alteration  in  the  system 
of  reactions  which  make  life  possible  may  cause  serious  results. 
Complete  universal  equilibrium  is  the  end  towards  which  we 
are  moving. 

Catalysis.  —  In  the  example  given  above  acetic  ester  in  the 
presence  of  water  decomposes  with  the  formation  of  alcohol  and 
acetic  acid.  The  rate  of  decomposition  is  slow,  but  if  a  small 
quantity  of  some  other  acid  is  added  the  reaction  goes  on  much 
faster.  The  acid  added  does  not  apparently  enter  into  the 
reaction  itself,  but  hastens  it  to  a  remarkable  degree.  The 
more  concentrated  the  acid  the  greater  the  velocity  of  the 
reaction.  Strong  acids  have  a  greater  effect  than  weak  acids 
and  experiments  have  shown  that  the  speed  of  the  reaction  is 
nearly  proportional  to  the  concentration  of  H  ions  in  the  solu- 


THEORY   OF  SOLUTIONS.  11 

tion.  The  action  of  the  acid  is  called  catalytic  and  the  acid 
itself  the  catalyzer. 

Catalyzers  do  not  enter  into  the  action  themselves,  but  a 
very  small  quantity  of  a  catalyzer  is  able  to  cause  a  large  effect 
upon  the  speed  of  reaction. 

The  physiological  chemist  is  chiefly  interested  in  the  cata- 
lytic action  of  the  enzymes  or  ferments  secreted  by  cells  with 
the  object  of  accelerating  reactions  which  are  of  use  to  them- 
selves. 

Colloids  and  Oryst-attoids.  —  Soluble  substances  are  divided 
into  two  groups,  the  basis  for  the  classification  being  their 
behavior  in  regard  to  diffusion. 

1.  Crystalloids  are  those  which  have  relatively  small  mole- 
cules and  readily  diffuse  through  a  membrane  such  as  parch- 
ment. 

2.  Colloids    possess    molecules   too   large   to   pass   readily 
through  pores  of  a  membrane,  so  diffuse  very  slowly  or  not  at 
all.     Proteid  molecules  for  instance. 

In  many  cases,  however,  it  is  not  the  actual  size  of  the 
molecules  which  prevents  diffusion,  but  the  fact  that  the 
molecules  cling  together  to  form  what  are  called  solution 
aggregates. 

Colloidal  Solutions  of  Metals.  —  It  has  been  found  pos- 
sible within  the  last  few  years  to  obtain  some  of  the  metals, 
gold,  silver,  platinum,  in  the  condition  of  a  colloidal  solu- 
tion. 

If  two  platinum  wires  carrying  a  strong  electric  current  are 
brought  close  together  below  the  surface  of  water  an  electric 
arc  will  be  formed.  Very  fine  pieces  of  platinum  are  torn  off 
from  the  cathode  (negative  pole)  and  the  solution  soon  has  a 
dark  brown  color.  No  pieces  of  platinum  can  be  seen  in  the 
liquid  even  under  the  highest  powers  of  the  microscope.  They 


12  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

exist  however  as  solution  aggregates,  not  as  individual  mole- 
cules. 

Such  metallic  colloidal  solutions  are  catalyzers  and  have  cer- 
tain similarities  to  enzymes. 

1.  A  very  small  quantity  of  metal  in  this  condition  can  cause 
a  great  change  in  the  speed  of  the  reaction. 


FIG.  2. 

2.  Certain  poisons  which  destroy  enzymes  have  an  analogous 
action  on  these  colloidal  solutions. 

AGGREGATION,  SUSPENSION,  AND  PRECIPITATION. 
The  solution  aggregates  being  minute  collections  of  molecules 
are  simply  small  lumps  of  the  substance.  In  various  ways, 
by  the  addition  of  salts  for  instance,  the  aggregates  can  be 
increased  in  size  so  that  several  cling  together.  More  and 
more  aggregates  attach  themselves  to  the  larger  lumps  until 
these  become  visible,  at  first  under  the  microscope  and  then  to 
the  eye,  forming  a  "  suspension."  Finally  the  lumps  become 
so  large  that  they  sink  and  the  colloid  is  "precipitated."  There 
is  then  no  real  difference  between  aggregation,  suspension  and 
precipitation.  They  are  only  different  stages  of  a  process. 


THEORY  OF  SOLUTIONS.  13 

OXIDATION  AND  KEDUCTION. 

1.  Oxidation  is  normally  the  addition  of  oxygen  to  some 
substance. 

Reduction  is  the  taking  away  of  oxygen  from  some  substance. 

Oxidizing  agents  are  substances  containing  a  large  amount  of 
oxygen  which  is  easily  set  free,  i.  e.,  it  is  in  loose  combination. 

Reducing  agents  are  substances  which  have  a  strong  affinity 
for  oxygen  and  combine  with  it  readily. 

The  above  definitions  are  not  sufficient  to  cover  the  case.  It 
is  a  general  rule  that  reduction  and  oxidation  go  on  simulta- 
neously but  in  different  substances. 

CuO  +  H2  =  Cu  +  H2O. 

The  copper  is  reduced,  the  hydrogen  oxidized. 

Copper  oxide  is  the  oxidizing  agent,  hydrogen  the  reducing 
agent. 

It  is  obvious  that  oxidation  and  reduction  go  on  simultane- 
ously in  cases  where  oxygen  is  taken  from  one  compound  by 
another.  One  is  oxidized,  the  other  reduced. 

2.  If  the  combining  power  of  a  metal  or  electro-positive  sub- 
stances, i.  e.,  substances  behaving  like  metals,  is  reduced,  this  is 
also  called  reduction. 

FeCl3  FeCl2 

Ferric  chloride          reduced  to  ferrous  chloride. 

In  the  first  instance  the  combining  power  of  Fe  is  with  3  Cl 
atoms,  in  the  second  it  only  combines  with  2  Cl  atoms. 

The  reverse  of  this  is  called  oxidation  for  convenience 
although  no  oxygen  is  added. 

FeCl2  FeCl3 

Ferrous  chloride          oxidized  to  ferric  chloride. 

3.  If  an   electro-negative  radical   is  taken  away  from  an 
electro-positive  radical  the  latter  is  reduced. 


14  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

Cobalt  (Co"1")  is  a  positive  radical,  being  a  metal. 
Chlorine  (Cl~)  is  a  negative  radical. 


/;  Cl-fH  i  -  >2HC1 
C\[C1±HJ 

The  cobalt  is  reduced,  the  negative  radical  being  removed. 
The  reverse  of  this  is  also  called  oxidation  for  convenience 


The  cobalt  is  oxidized  to  CoCl2. 

In  the  first  case  the  hydrogen  is  oxidized  to  HC1. 

Hydrogen  is  a  reducer.  —  At  the  moment  of  being  freed 
from  combination  it  is  said  to  be  nascent  and  is  then  a  much 
more  active  reducer,  i.  6.,  combines  more  readily,  than  when  in 
the  gaseous  condition.  In  the  gaseous  condition  it  exists  as  a 
molecule  and  may  be  represented  by  the  formula  H  —  H  or  H2 
whilst  nascent  hydrogen  is  in  the  atomic  form  H~. 

We  may  pass  gaseous  hydrogen  through  a  solution  of  ferric 
chloride  for  a  long  time  without  reducing  it  to  the  ferrous 
state,  but  on  adding  acid  and  then  some  zinc  to  the  solution, 
(H2SO4  +  Zn  ==  ZnSO4  +  H  +  H),  hydrogen  is  set  free  in  the 
nascent  condition  and  the  ferric  chloride  quickly  reduced  : 

FeCl3  +  H  =  FeCl2  +  HCL 

A  very  ready  means  for  obtaining  nascent  hydrogen  in 
aqueous  solutions  is  by  the  use  of  sodium  or  sodium  amalgam. 

Na  -f  H2O  =  NaOH  +  H. 

Oxygen.  —  The  oxygen  of  the  atmosphere  is  in  the  molecular 
condition  O  =  O  or  O2. 

Nascent  oxygen  may  be  obtained  by  the  decomposition  of 
hydrogen  peroxide,  H2O2  =  H2O  -f  O,  or  by  the  decomposi- 
tion of  water  by  chlorine,  H2O  -f  C12  =  2HC1  +  O. 


THEORY    OF   SOLUTIONS. 


15 


Ozone  is  an  allotropic  form  of  oxygen  represented  by  the 
formula 

A 

It  decomposes  very  readily,  yielding  nascent  oxygen  and  is 
therefore  a  very  active  oxidizing  agent. 

AUotropism  is  a  term  used  to  denote  the  existence  of  the 
same  element  in  different  physical  forms.  These  forms  are 
probably  due  to  a  different  atomic  arrangement  in  the  mole- 
cule. Carbon,  sulphur,  phosphorus  and  oxygen  are  prominent 
elements  in  living  matter 
and  have  allotropic  forms. 

OSMOTIC  PRESSURE. 

Matter  in  the  gaseous 
form  is  in  much  the  same 
condition  as  when  in  a  solu- 
tion. In  both  cases  the 
molecules  are  free  to  move 
about,  and  in  both  cases  the 
movement  expresses  itself  as 
a  pressure.  The  pressure 
exerted  by  a  gas  is  familiar 
to  all.  The  analogous  pres- 
sure of  the  substance  in 
solution,  although  more  dif- 
ficult to  measure,  obeys  the 
same  laws.  It  is  called  the 
osmotic  pressure. 

This  was  first  demonstra- 
ted by  filling  a  bladder  with  alcohol  and  then  immersing  it  in 
water.     The  water  can  pass  in,  but  the  alcohol  cannot  pass  out 


A   Porous  cup  contaln- 

,ing  sugar  solution 
B    Jar  of  water 
C   Pressure  tube 

FIG.  3. 


16  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

to  any  extent,  and  the  increased  pressure  will  cause  the  bladder 
to  burst. 

The  demonstration  of  osmotic  pressure  requires  a  semi- 
permeable  membrane,  i.  e.,  a  membrane  permeable  to  the  sol- 
vent, but  not  to  the  dissolved  substance. 

Such  a  membrane  may  be  prepared  by  precipitating  copper 
ferrocyanide  in  an  unglazed  earthenware  cup.  If  such  a  cup  is 
filled  with  a  sugar  solution,  attached  to  a  manometer  and  then 
immersed  in  a  jar  of  water  the  manometer  will  soon  indicate  a 
rise  of  pressure  in  the  cup.  This  pressure  will  continue  to  in- 
crease until  the  final  pressure  will  be  the  same  as  it  would  be 
if  the  dissolved  substance  were  a  gas  and  occupied  the  same 
volume  as  the  sugar  solution. 

The  pressure  attained  depends  upon  the  concentration  and 
temperature  of  the  solution.  The  explanation  of  gas  pressure 
in  terms  of  the  kinetic  theory  is  that  it  is  due  to  a  bombard- 
ment of  the  walls  of  the  confining  vessel  with  particles  of  gas 
but  there  is  no  satisfactory  explanation  of  the  cause  of  osmotic 
pressure. 

The  many  problems  of  filtration,  secretion  and  absorption  in 
the  body  have  caused  physiologists  to  be  very  much  interested 
in  the  phenomena  of  osmotic  pressure. 

CALCULATIONS  OF  A  FORMULA. 

To  calculate  the  formula  of  a  compound  two  things  must  be 
known : 

1.  The  molecular  weight. 

2.  The  percentage  composition. 

The  molecular  weight  may  be  determined  by  : 

1.  Measuring  the  elevation  in  boiling  point  or  depression  in 

freezing  point  caused  by  dissolving  a  known  amount  of  the 

compound  in  a  known  amount  of  liquid. 


THEORY   OF   SOLUTIONS. 
' 


" 


- 

2.  By  determining  its  vapor  density,  provioitrg--itiwifl  vola- 
tilize without  decomposition. 

3.  Other  methods  which  cannot  be  described. 

The  percentage  composition  is  determined  by  ultimate  analy- 
sis of  a  pure  sample  of  the  compound. 

Suppose  we  have  a  compound  with  a  molecular  weight  180, 
percentage  composition 

C  —  40     per  cent. 

H  -  6.66 

O  -  53.3        " 

The  percentage  of  each  element  is  divided  by  the  atomic 
weight  of  that  element. 

C  -  40/12  -  3.33  1 
H-  6.66/1  -6.66  2 
O  -  533/16  -  3.33  1 

Express  the  ratio  in  whole  numbers  and  the  simplest  formula 
for  the  given  substance  would  be  CH2O  which  would  have  a 
molecular  weight  of  30.  The  compound  in  question  had  a 
molecular  weight  of  180  so  it  must  be  six  times  as  large  as  the 
simpler  one  or  C6H12O6. 

The  difficulty  of  determining  the  molecular  weight  of  many 
substances  prevents  an  empirical  formula  from  being  exactly 
determined.  Two  substances  may  have  the  same  percentage 
composition  and  yet  have  a  very  different  molecular  weight,  as 
in  the  example  given  above,  formaldehyde  and  dextrose. 

The  empirical  formula  of  a  compound  shows  the  number  of 
atoms  of  different  elements  there  may  be  in  a  molecule  but  it 
does  not  show  their  arrangement.  The  behavior  of  any  com- 
pound is  much  more  intelligible  if  we  know  how  the  different 
atoms  are  combined.  This  atomic  arrangement  is  shown  by 
the  graphic  formula  : 
2 


18  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

H2SO4    empirical  formula. 

(1)  g^       graphic  formula. 


There  are  obviously  other  ways  of  arranging  the  atoms  in  this 
case, 

X0          Q  H 

(2)  \(]  or  (3) 

H7 

Sulphur  may  have  a  valence  of  4  or  6,  oxygen  always  being 
2,  hydrogen  1.  There  are  many  reasons  why  formula  1  is  to 
be  regarded  as  correct.  In  the  first  place  compounds  having 
oxygen  combined  with  itself  are  very  unstable 

H202,     H-O-O-H, 

or  O3  ozone  /  \ 

Sulphuric  acid  is  very  stable,  therefore  it  cannot  be  either 
(2)  or  (3). 

For  the  same  reasons  HNO3  is  written 

^° 


and  HC1O,,, 

„/> 

_tL — O —  v- '1\. 

\> 

Cl  when  oxidized  may  have  1,  3,  or  5  valences. 


THEORY    OF    SOLUTIONS.  19 

There  are  reasons  also  for  believing  that  the  hydrogen  is  tied 
to  the  sulphur  by  means  of  oxygen. 


SO,, 
combines  with  chlorine  to  form  a  compound 


this  reacts  with  water  to  form  sulphuric  acid. 
H—  O—  ("H  ajx^ 

H-o-[H.aj/ 

REASONS  WHY  REACTIONS  TAKE  PLACE. 
An  old  rule  which  applies  to  a  large  number  of  cases  is  the 
following  :  "  Whenever  an  insoluble  or  volatile  substance  can 
be  formed,  it  will  be  formed  to  the  full  extent  of  the  compo- 
nents." As  an  example  we  may  consider  the  decomposition  of 
calcium  carbonate  by  heat  : 

CaCO3  ^"^  CaO  +  CO2. 

CO2  is  volatile  and  as  long  as  there  is  no  hindrance  to  its  escape 
the  decomposition  continues.  If,  however,  the  calcium  carbo- 
nate is  heated  in  a  strong  closed  steel  cylinder  so  that  the  CO2 
cannot  escape,  the  calcium  carbonate  is  found  unchanged  when 
the  cylinder  is  opened  after  cooling. 

The  reactions  which  are  used  in  ultimate  analysis  obey  this 
law.  In  determining  the  amount  of  sulphur  in  organic  sub- 
stances the  sulphur  is  oxidized  to  a  sulphate  which  is  precipi- 
tated by  some  soluble  salt  of  barium,  such  as  the  chloride. 

,  +  BaCl2          2  Nad  +  BaS04 


20  OUTLINES    OF    PHYSIOLOGICAL   CHEMISTRY. 

The  BaSO4  is  almost  completely  insoluble  and  is  therefore 
removed  from  the  solution.  By  adding  an  excess  of  barium 
all  the  sulphate  will  be  precipitated.  The  reaction  will  run  to 
an  end  practically. 

This  is  a  case  where  the  equilibrium  is  at  vanishing  point. 

A  few  graphic  formulas  of  inorganic  compounds  which  will 
be  of  use  are  given.  They  will  serve  also  as  an  introduction 
to  the  numerous  graphic  formulas  of  organic  compounds  with 
which  we  shall  have  to  deal. 

Fe,  2  or  4  valences,  Cl,  1  valence. 

Cl 


Cl 

a 

Fe^-Cl 
\C1 

Ferric  chloride,  Fe2Cl6,  usually  written  FeCl3.  Ferrous  chloride,  FeCl2. 

Basis  for  ferri  compounds.  Basis  for  ferro  compounds. 

S,  2,  4  or  6  valences,     H,  1  valence,         O,  2  valences. 

,H  O  O 

H-O-S-O-H  H-O-S-O-H 

II 

O 
Hydrosulphuric  acid.  Sulphurous  acid.  Sulphuric  acid. 

Ba,  2  valences,     Ca,  2  valences. 

/O— H 
Ba<  Ba<^  Ba< 


/Cl 
< 
\C1 


Barium  hydroxide.         Barium  chloride.  Barium  sulphate, 

Calcium  (Ca)  combines  in  the  same  way. 

Ky  1  valence,         Na,  1  valence. 
O  O 


H-0-S-O-K 

O 

Monopotassic  sulphate, 
KHSO4 

K-O-S-O-K 
O 

Dipotassic  sulphate, 
K2S04 

Na  combines  in  the  same  way. 
P,  3  or  5  valences. 


THEORY   OF   SOLUTIONS.  21 

H—  <K  0=P=0 

H-0—  P=0  O/ 

H-0/  0=£=0 

Phosphoric  acid,  Phosphoric  anhydride, 

H3PO«  P208 

Phosphoric  anhydride  is  two  molecules  of  H3PO4  from  which 
three  molecules  of  H2O  have  been  driven  off. 
P206+3H20=2H3P04 
N9  3  or  5  valences. 


H-N-H  >N— O— H  H  — O  — N  =  O  H— O— 


Ammonia  gas,    Ammonium  hydroxide,  Nitrous  acid,  Nitric  acid, 

NH8  NH,iOH(OH-  ion)  HNO2(H+ion)  HNO3(H+ion). 


ULTIMATE  ANALYSIS. 

The  determination  of  the  elementary  content  of  any  substance 
is  called  ultimate  analysis. 

The  elements  which  occur  in  proteid  and  are  therefore  of 
most  interest  to  us  are  C,  O,  H,  P,  S  and  N. 

The  first  three  of  these  are  estimated  in  various  ways,  but 
hardly  concern  us  since  it  is  only  exceptionally  that  determina- 
tions of  C,  O  and  H  content  of  proteid  are  made.  P,  S  and  N 
estimations  however  are  constantly  required. 

P  Content.  —  The  P  in  the  substance  is  oxidized  to  phos- 
phoric acid  and  precipitated  as  insoluble  magnesium  phosphate 
and  the  amount  of  P  calculated.  In  the  words  of  the  chemist 
it  is  estimated  as  P2O5. 

8  Content.  —  The  sulphur  is  completely  oxidized  to  sulphuric 
acid  or  soluble  sulphates,  then  precipitated  as  the  insoluble 
BaSO4,  which  is  weighed  and  the  amount  of  S  calculated. 
Estimated  as  barium  sulphate. 

N  Content.  —  N  is  estimated  as  NH3  by  KjeldahPs  method. 
(see  text-books). 


CHAPTER  II. 

ORGANIC  CHEMISTRY  OR  THE  CHEMISTRY  OF 
CARBON  COMPOUNDS. 

THE  element  carbon  differs  from  other  elements  in  its  re- 
markable power  of  combining  with  itself  to  form  stable  com- 
pounds. Its  combining  power  or  valence  is  determined  by  an 
analysis  of  many  of  its  simplest  compounds  to  be  4,  i.  e.,  it  .can 
combine  with  four  atoms  of  hydrogen. 

If  we  consider  the  structure  of  the  compounds  of  hydrogen 
and  oxygen,  H2O  and  H2O2  we  see  a  reason  for  the  difference 
in  properties  due  to  the  fact  that  oxygen  is  combined  with 
itself.  H  —  O  —  H  is  one  of  the  most  stable  compounds 
known.  H  —  O  —  O  —  H  is  very  readily  decomposed,  the 
element  of  weakness  being  the  tie  between  the  O  atoms. 

Again  the  diazo  compounds  which  contain  the  atom  group 
—  N  =  N  —  are  very  explosive,  i.  6.,  the  compound  is  unstable, 
the  two  N"  atoms  being  easily  separated.  But  carbon  may  com- 
bine with  itself  (C  —  C  —  C  —  C)  to  an  almost  unlimited  extent, 
and  still  form  stable  compounds. 

It  is  this  property  of  the  C  atom  which  makes  possible  the 
immense  and  complicated  molecules  of  organic  matter. 

The  simplest  compounds  of  carbon  are  the  hydrocarbons, 
substances  which  contain  only  carbon  and  hydrogen.  The 
simplest  of  the  hydrocarbons  is  represented  by  the  formula  CH4. 
Because  of  the  large  number  of  hydrocarbons  and  their  great 
variation  in  structure  it  is  necessary  to  arrange  the  atoms 
graphically  in  order  to  grasp  the  full  significance  of  their  con- 
struction. The  graphic  formula  of  CH4  may  be  thus  written 

22 


ORGANIC  CHEMISTRY.  23 


H— C— H 

H 

Methane  (marsh  gaa). 

Methane  is  the  simplest  of  a  series  of  compounds  called  the 
methane  or  marsh  gas  series  of  hydrpcarbons. 

The  H  atoms  may  be  replaced  by  other  elements,  forming 
what  are  called  substitution  products.  For  instance  if  chlorine 
is  mixed  with  methane  in  equal  volume  and  exposed  to  sun- 
light, a  reaction  which  may  be  represented  as  follows,  takes 

place. 

H          H     01  H          H 

">c/  ±|  —  >HCI+   \c/ 
H        in    cij  H        ci 

Methane  +  chlorine  =  hydrochloric  acid  +  monochlonnethane. 
CH,  +  Cla       =  HC1  +  CH3C1 

On  increasing  the  amount   of  chlorine   the   change   may  go 

further 

H         H     Cl  H         H 

X-±JL— >HC1+  >°\ 

ci       IL.CIJ  ci       ci 

Monochlormethane.  Dichlormethane. 

CH3C1  +  C12  =  HQ  +  CHjCl, 

By  continued  action  a  series  of  chlorine  substitution  products 
of  methane  are  formed. 

CH3C1  Monochlormethane, 

CH2C12  Dichlormethane, 

CHC13  Trichlormethane, 

CC14  Tetrachlormethane. 

In  the  same  way  iodine  and  bromine  substitution  products 
may  be  formed. 


24  OUTLINES    OF   PHYSIOLOGICAL   CHEMISTRY. 

These  compounds  are  said  to  be  saturated  because  the  maxi- 
mum combining  power  of  the  C  atom  is  used. 

The  next  in  this  series  of  hydrocarbons  contains  two  atoms 
of  carbon  held  together  by  a  single  bond,  the  three  remaining 
valences  of  each  C  atom  being  brought  to  saturation  by  hydro- 
gen. The  only  possible  way  of  representing  this  graphically 
is  by  the  formula 

H— C— H 
H— C— H 

H 

Ethane,  CaHe. 

Ethane  is  a  gas  having  much  the  same  chemical  behavior  as 
methane.  We  may  consider  it  as  a  substitution  product  of 
methane,  formed  by  substituting  a  methyl  group,  CH3,  for  one 
of  its  H  atoms.  In  the  same  way  a  methyl  group  if  substituted 
in  ethane,  gives  propane,  the  next  higher  compound  of  the 
series. 


Propane,  C3H8  or  CH3  .CHa  .CH, . 

It  is  evident  from  the  graphic  formula  of  propane  that  the 
central  C  group  differs  from  the  other  two,  and  therefore,  on 
forming  the  next  higher  compound  of  the  series  it  will  make  a 
difference  whether  we  substitute  the  methyl  group  on  one  of  the 
C  atoms  at  the  end  of  the  chain  or  the  central  one.  We  may 
thus  form  two  hydrocarbons  having  the  formula  C4H10(butane), 
but  differing  in  the  arrangement  of  the  groups. 


ORGANIC   CHEMISTRY.  25 


Normal  butane,  C4H10.  Iso-butane,  C4H10. 

The  two  compounds,  although  they  have  precisely  the  same 
amount  of  C  and  H,  present  different  characteristics  —  reac- 
tions, appearance,  odor,  etc.  —  which  can  only  be  explained  on 
the  basis  of  differing  internal  arrangement. 

Such  compounds  are  said  to  be  isomers  and  as  we  go  higher 
in  the  series  the  number  of  possible  arrangements  and  conse- 
quently the  number  of  isomers  increases  with  alarming  rapidity. 
Methane  CH4  -  1     Pentane  C5H12  -  3    Octane  C8H18  -  18 
Ethane     C2H6  -  1    Hexane  C6H14  -  5    Nonane  C^  -  35 
Propane    C3H8  —  1    Heptane  C7H16  —  8    Decane  C^H^  —  75 
Butane     C4H10  -  2 

A  common  difference  CH2  exists  between  the  successive 
members  so  that  a  general  formula  for  the  series  may  be  given 
«  C»H2n+2. 

The  hydrocarbons  are  such  inactive  bodies  chemically  that 
they  are  of  no  particular  interest  to  us  except  to  take  as  simple 
examples  with  a  view  to  gaining  some  elementary  ideas  of  the 
structure  of  organic  compounds.  The  lower  (those  with  a  few 
C  atoms)  members  of  the  series  are  gases,  and  as  the  molecular 
weight  increases  the  boiling  point  rises ;  the  higher  members 
being  the  wax-like  bodies  called  paraffins. 

Such  a  series  as  that  given  above  in  which  there  is  a  simi- 
larity in  constitution  but  a  gradual  and  regularly  increasing 
variation  in  properties  is  said  to  be  homologous,  and  the  mem- 
bers are  called  homologues. 


26  OUTLINES    OF   PHYSIOLOGICAL   CHEMISTRY. 

Example  :  Butane,  C4H10,  is  a  higher  homologue  of  propane, 


There  are  many  such  series  among  the  organic  compounds. 

By  oxidation  of  the  hydrocarbons  a  number  of  interesting 
and  well-known  compounds,  the  alcohols,  aldehydes  and  organic 
acids  are  obtained. 

We  can  now  trace  in  regular  sequence  the  processes  of  oxi- 
dation and  the  compounds  resulting  from  it. 

ALCOHOLS,  ALDEHYDES,  ACIDS. 

1  .  Alcohols.  —  If  methane  is  completely  oxidized  the  result 
is  the  formation  of  carbon  dioxide  and  water. 


If  the  oxidation  is  carefully  regulated  however  the  inter- 
mediate products  in  the  process  may  be  obtained.  We  may 
thus  introduce  one  O  atom  into  the  methane  molecule 


=          H— C— 0— H 


In  this  new  substance  the  H  atom  which  is  tied  to  the  carbon 
through  the  oxygen  atom  behaves  very  differently  from  the 
remaining  three,  being  much  more  easily  split  off,  thus  allow- 
ing the  O  to  attach  itself  to  other  compounds.  In  other  words 
the  new  compound  is  chemically  active  whilst  the  hydrocarbons 
are  chemically  inert. 

The  substance  CH3OH  is  the  simplest  of  a  new  homologous 
series  of  compounds  obtained  by  partially  oxidizing  the  hydro- 
carbons. These  are  the  alcohols,  the  one  already  given  being 
methanol  (methyl  alcohol),  commonly  called  wood  alcohol  be- 
cause it  is  obtained  by  the  dry  distillation  of  wood. 


ORGANIC   CHEMISTRY.  27 

The  alcohols  are  always  designated  by  the  suffix  "  ol." 


H—  C—  O—  H 

H-C—  0—  H 
H—  C—  H 

H—  C—  O—  H 
H-C—  H 
H—  C—  H 

Butanol  and 
higher 
homologues. 

A 

H 

H 

Methanol  (methyl 
alcohol),  CH3OH. 

Ethanol  (ethyl  alcohol), 

Propanol  (propyl 
alcohol),  C3HTOH. 

General  formula  CnH2n+1OH. 

The  alcohol  of  everyday  use  is  ethanol  or  ethyl  alcohol 
obtained  as  a  product  of  fermentation. 

The  alcohols  exist  in  isomeric  forms  but  since  two  or  more 
isomeric  alcohols  may  be  derived  from  one  hydrocarbon  the 
number  of  isomers  is  vastly  greater.  Fortunately  only  a  few 
are  of  importance  for  us. 

Alcohols  are  divided  into  three  classes,  primary,  secondary 
and  tertiary,  the  basis  of  the  classification  being  the  arrange- 
ment of  the  molecule.  This  may  be  illustrated  by  the  butyl 
alcohols  C4H9OH. 


QH, 

CH2OH 

Normal  butane,  C4H10.        Primary  normal  butanol 
(primary  butyl  alcohol), 


CHS 


Secondary  normal  butanol 
(secondary  butyl  alcohol), 
C4H9OH. 


COH 
CH, 


Iso  butane, 
C4H10. 


Primary  iso  butanol  (primary        Tertiary  butanol  (tertiary 
butyl-alcohol),  C4H9OH.     '          butyl-alcohol),  C4H8OH. 


28  OUTLINES  OF  PHYSIOLOGICAL  CHEMISTEY. 

GROUPS  CHARACTERISTIC  OF  ALCOHOLS. 


(1) 

E—  CH2OH 

Primary 

(2) 

^CHOH 
E/ 

Secondary. 

(3) 

X 
E-)COH 

W 

Tertiary. 

2.  Aldehydes,  Ketones.  —  The  alcohols  have  different  char- 
acteristics, but  the  differences  in  their  oxidation  products  is 
more  striking. 

A.  Primary  alcohols  on  further  oxidation  yield  aldehydes. 


E— c— O— H 

t 


But  since  the  C  atom  can  never  support  more  than  one 
chemically  active  (OH)  group,  this  combination  is  an  impossi- 
bility, so  something  must  happen.  H2O  is  immediately  thrown 
off  and  the  C  attaches  itself  to  the  remaining  O  by  two  valences. 


E-C-0—  iH 

=           B-e=:0+] 

A  ! 

Aldehyde. 

1 

The  group  CHO  is  characteristic  of  aldehydes. 
B.  Secondary  alcohols,  on  oxidation  yield  ketones. 


ORGANIC  CHEMISTRY.  29 

Again  H2O  is  thrown  off  and  we  get 


Ketone. 


The  group  CO  is  characteristic  of  ketones. 
Since  the  tertiary  alcohols  have  the  formula 


E— COH 

there  is  obviously  no  H  left  for  oxidation.  If  the  COH  group 
is  further  oxidized  to  C  =  O,  the  C  atom  must  take  a  valence 
from  one  of  the  radicals,  so  that  the  compound  would  break  up. 
The  aldehydes  are  always  designated  by  the  suffix  "al." 
Thus  we  have : 

H— C=O  H— C=O  H— C=O 

iY  ATT  Atr  Butanal  and 

^^3  Vn2  higher  homologues. 

ATT 

LJ13 

Methanal  Ethanal  Propanal 

-  ,,  (progtaic.Meh.de), 


Formalin  is  the  commercial  formaldehyde  40  per  cent,  in 
water. 

The  Ketones  obviously  cannot  exist  unless  the  chain  contains 
three  or  more  C  atoms.  They  always  have  the  suffix  "  one." 


Pentanone  and  higher 
homologues. 


H3 

Propanone  (acetone),  Butanone, 

CaH6 .  CO.  C3H8  .  CO. 


i— C— H 


30  OUTLINES    OF   PHYSIOLOGICAL   CHEMISTRY. 

3.  Acids. — The  aldehydes 

K- 
have  one  H  left  which  can  be  oxidized  to  form  an  acid. 

K— C-H     -fO  K— C— O-H 

Aldehyde.  Acid. 

Acids  always  have  the  suffix  acid  so  we  have  — 

O=Q—  O— H 

Bu1 

homologues. 


Butanacid  (butyric 

O==C-O-H        O=C-O-H  fcn,  "ffiSSC* 


H  CH3  CH3 

Methanacid  (formic        Ethanacid  (acetic         Propanacid  (propionic 
acid),  HCOOH.  acid),  CH3  .  COOH.         acid),  C3H6 .  COOH. 

General  formula  CnH2nO2. 

The  group  COOH  is  characteristic  of  the  acids. 

The  Ketones 


have  no  H  left  for  oxidation.     On  further  oxidation  the  com- 
pound breaks  up.     Summarizing 

On  oxidation. 

Primary  alcohols  »->•  Aldehydes  m-*-  Acids  »->-  Break  up. 
Secondary  alcohols  »-»-  Ketones     »->•  Break  up. 
Tertiary  alcohols  a->-  Break  up. 

Acids  then  can  only  be  derived  from  primary  alcohols, 
(CH2OH)  the  series  so  formed  being  called  the  Fatty  acid  series, 
since  certain  of  the  higher  homologues  encer  into  the  composi- 
tion of  the  fats. 

The  members  of  the  fatty  acids  series  are  monobasic,  since 
there  is  only  one  OH  group  to  enter  into  combination. 


ORGANIC   CHEMISTRY. 

A  comparison  may  be  made  with  the  mineral  acids. 
K— c— O— H  O 


31 


H-0-S-O-H 


Fatty  acid  monobasic.       Nitric  acid  monobasic.         Sulphuric  acid  dibasic. 


The  following  table  summarizes  the  four  homologous  series  so 
far  discussed. 


Chemically 
Inert. 

Chemically  Active. 

Basic.                       Neutral.                      Acid. 

General 
Prefix. 

Hydro- 
carbons. 

Alcohols. 
Suffix  "ol." 

Aldehydes. 
Suffix  ''  al." 

Acids. 
Suffix  "acid." 

Meth. 
Eth. 
Prop. 
But. 

CH< 

•§!: 

C^HIO 

CH8OH 
C2H5OH 
CsH7OH 
C4H9OH 

H.CHO 
CH3.CHO 
CjHoCHO 
CaHj.CHO 

H.COOH 
CH,.COOH 
C3H6.COOH 
CSH7.COOH 

and  so  on  for  the  higher  homologues,  which  are  designated  by 
the  number  of  C  atoms  they  contain  —  Pent.,  Hex.,  Hept.,  etc. 
A  study  of  the  table  brings  out  some  interesting  points. 

1.  The   introduction  of  O   changes   chemically  inert   into 
chemically  active  compounds.     This  rule  is  not  universal  but 
holds  good  for  many  organic  compounds. 

2.  The  introduction  of  a  little  O  produces  basic  alcohols 
which  will  readily  unite  with  acids  : 

Example : 


HaC-:0-H    Hi 

f 

-     O 


CH, 


JLC-O-NO, 


CH. 

O=N=O 

Ethyl  alcohol  +  Nitric  acid  =  Ethyl  nitrate  +  water. 


+H,0 


The  alcohols  of  this  series  have  only  one  active  OH  group, 
so  are  called  monoatomic. 


32  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTEY. 

3.  The  introduction  of  a  little  more  O  produces  neutral  alde- 
hydes, which  have  no  special  affinity  for  either  acids  or  bases, 
but  being  chemically  active  afford  some  very  interesting  reac- 
tions with  various  organic  compounds. 

These  reactions  will  have  to  be  discussed  later  since  they 
occur  with  complex  substances,  the  constitution  of  which  has 
not  yet  been  considered.  The  reaction  with  Fehling's  solution, 
h'owever,  will  be  explained  directly. 

4.  The  introduction  of  a  further  amount  of  O  produces  acids 
which  will  readily  combine  with  a  base. 

Example  : 


A 


_K 


Acetic  acid  +  Potassium  hydroxide  =  Potassium  acetate  +  water 
CH,  •  COOH  KOH  CH3  .  COOK 

It  has  been  explained  in  Chapter  I.  that  an  increase  of  O 
does  not  necessarily  mean  an  increase  of  acidity,  but  with 
organic  compounds  this  is  nearly  always  the  case. 

It  may  however  be  remarked  that  the  alcohols  are  weak 
bases  and  the  fatty  acids  weak  acids. 

1.  An  alcohol  in  combination  with  an  acid  is  easily  driven 
out  by  a  strong  mineral  base  such  as  KOH. 

Example  : 

CH3  •  CH2—  O—  NO2    +    KOH    =    K—  O—  NO2    +    CH3  -  CH2OH 

Ethyl  nitrate  +  Potassium  hydroxide  =  Potassium  nitrate  +       Ethyl  alcohol. 

2.  A  fatty  acid  in  combination  with  a  base  is  easily  driven 
off  by  a  strong  mineral  acid. 

Example  : 

CH3  •  COOK      -f      HONO2     =          KONO2  +    CH3  .  COOH 

Potassium  acetate      -j-      Nitric  acid      =      Potassium  nitrate       +         Acetic  acid. 


ORGANIC  CHEMISTRY.  33 

TESTS. 

1.  For  Alcohols.  —  lodoform  test,  see  p.  54. 

2.  For  Aldehydes.  —  The  aldehydes  representing  an  inter- 
mediate stage  of  oxidation  are  always  eager  for  more  O,  and 
take  it  up  whenever  it  is  offered  in  an  accessible  form. 

They  will  therefore  seize  O  from  other  compounds  in  cases 
where  the  latter  carry  it  loosely.  Such  a  compound  is  found 
in  cupric  hydroxide.  Aldehydes  therefore  are  reducers.  In 
cases  where  it  is  required  to  deprive  certain  compounds  of  their 
oxygen,  or  a  part  of  it,  the  aldehydes  are  often  employed  for 
this  purpose. 

CHEMISTRY  OF  FEELING'S  SOLUTION. 
Copper  has    two  hydroxides    and  corresponding    insoluble 
oxides. 

Cu— O— H  Cuv  ,O— H 

>O  Cu<  Cu=O 

Cu— O— H  Cu/  \O— H 

Cuprous  hydroxide         Cuprous  oxide  Cupric  hydroxide         Cupric  oxide 

yellow.  red.  blue.  black. 

Cupric  hydroxide,  C^OH)^  is  blue  when  first  precipitated. 
On  adding  alkali  (KOH)  and  boiling,  H2O  is  driven  off  and 
black  cupric  oxide  CuO  which  is  insoluble  is  formed  and  falls 
as  a  precipitate. 

Cu(OH)2  =  CuO  +  H20. 

But  if  Cu(OH)2  is  heated  with  a  reducing  agent  such  as  an 
aldehyde  (glucose  is  an  aldehyde),  the  cupric  hydroxide  decom- 
poses still  further  to  cuprous  oxide. 

2Cu(OH)2  =  Cu2O  +  H2O  +  O, 

the  O  being  taken  up  by  the  reducer. 

The  bright  red  Cu2O  is  insoluble  and  this  is  the  red  precipi- 
tate which  is  looked  for  on  testing  solutions  for  the  presence 
of  reducers  —  glucose,  etc. 
3 


34  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

But  unless  there  is  enough  reducer  to  change  all  the  cupric 
hydroxide  into  red  cuprous  oxide,  some  of  it  will  precipitate  as 
black  cupric  oxide  which  masks  the  red  color.  To  avoid  this 
tartaric  acid  is  used,  which  forms  a  soluble  colorless  compound 
with  the  cupric  oxide  but  does  not  affect  the  red  cuprous  oxide. 

The  point  is  to  add  something  by  which  the  CuO  is  made 
soluble  and  colorless,  but  which  leaves  the  Cu2O  unchanged. 

Fehling's  solution  A  is  CuSO4. 

Fehling's  solution  B  is  KOH  -f  some  tartrate. 

On  mixing  the  two  the  following  reaction  occurs  : 

CuS04  +  2KOH  =  K2S04  +  Cu(OH)2 

The  Cu(OH)2  must  be  used  fresh  as  it  decomposes  slowly  in 
the  cold,  so  the  two  solutions  are  not  mixed  until  just  before 
using. 

Nylander's  Test.  —  Glucose  and  other  aldehydes  reduce  other 
metallic  oxides  in  alkaline  solution.  The  reduction  of  bismuth 
oxide  is  the  basis  for  Nylander's  test.  In  this  case  the  metallic 
oxide  in  alkaline  solution  will  keep  for  months.  In  boiling 
with  a  reducing  substance  a  black  deposit  of  bismuth  is  formed. 

The  Ketones  (CO)  have  no  spare  H  for  oxidation  so  are  not 
greedy  for  O,  and  do  not  reduce  copper  oxide.  The  reaction 
with  Fehling's  solution  is  therefore  an  aldehyde,  not  a  ketone 
reaction. 

3.  For  Acids.  —  Treated  with  FeCl3  the  lower  (homologues 
of  the)  fatty  acids  and  their  salts, — formates,  acetates,  etc.,  afford 
a  red  color  due  to  the  formation  of  colored  Fe  compounds.  The 
reaction  is  not  well  understood  and  need  not  be  discussed  in 
detail. 

UNSATURATED  COMPOUNDS. 

In  addition  to  the  homologous  series  already  discussed  there 
are  others  called  unsaturated  compounds,  in  which  two  C  atoms 


ORGANIC   CHEMISTRY.  35 

are  joined  by  two  or  three  links  instead  of  one.     The  hydro- 
carbons of  such  series  have  the  suffix  ene  and  ine. 

Clia  CU« 

CHg  CHj  OH 

Ethane.  Ethene  (ethylene  gas).    Ethine  (acetylene  gas). 


SH 
I 

CHa 


Propine. 

These  likewise  form  long  series  of  oxidation  and  substitution 
products  but  the  compounds  formed  are  of  little  interest  to 
physiological  chemists,  who  do  not  deal  in  gases  and  mineral 
oils. 

It  will  be  noticed  that  in  these  compounds  the  C  atom  always 
has  four  occupied  links,  but  since  in  the  unsaturated  hydro- 
carbons there  are  two  adjacent  carbon  atoms  united  doubly  or 
trebly  to  each  other  the  ratio  of  hydrogen  to  carbon  is  smaller 
than  in  the  saturated  series. 

THE  CARBON  MOLECULE. 

The  C  atom  can  attach  itself  to  another  or  to  two  others  by 
all  of  its  four  valences,  thus  forming  the  carbon  molecule. 
Three  forms  of  allotropism  are  possible  which  are  probably 
represented  by  charcoal,  graphite  and  diamond. 

C 
i\ 

/~i  /"t  /~i       /"^ 

ml  XV  %/ 

C/^i  fN  Vi 

\jn "         \j  \j 

123 

Only  one  grouping  is  possible  with  1,  but  it  is  obvious  that 
the  rings  2  and  3  can  theoretically  contain  an  unlimited  num- 
ber of  carbon  atoms,  but  nothing  is  known  of  the  way  in 
which  the  carbon  atoms  hang  together  to  form  the  molecule. 


CHAPTER   III. 

COMBINATIONS  OF  THE  OXIDATION  PRODUCTS  OF  THE 
PARAFFINS  WITH  EACH   OTHER. 

ETHERS,  ESTERS,  ANHYDRIDS. 

THE  ethers  are  the  result  of  a  reaction  between  the  OH 
groups  of  two  alcohols  with  loss  of  water ;  in  other  words  of 
two  bases.     Strong  mineral  bases  cannot  do  this,  but  weak 
organic  bases  are  able  to. 
Example. 

Ethanol.  CH3  •  CH20  j""H  j  CH3  •  CH2 

+  ^>0+H20 

Ethanol.  CH,-CH2    I  OH  |  CH3-CH2 

Ethanether  (ether). 

The  alcohols  which  enter  into  the  combination  are  not  neces- 
sarily similar.  The  ether  may  be  methyl  ethyl,  or  ethyl 

propyl,  etc. 

CHj  CH3 

>° 

CH8-CH2  CH3-CH2-CH2 

The  ether  of  the  laboratory  is  ethyl  ether,  often  called  sul- 
phuric ether,  although  there  is  no  sulphuric  acid  in  its  compo- 
sition. Sulphuric  acid,  however,  is  employed  in  its  manufacture 
from  alcohol. 

The  reaction  occurs  in  two  stages  : 

CH3.CH2JOH1 

ft  I) 

+  |    Hi— O— S— O— H         =         CH3  •  CEL— O— S— O-H+H-O 

O  £> 

Alcohol  +  Sulphuric  acid.  Ethyl  sulphuric  acifi. 

36 


OXIDATION   PRODUCTS   OF   THE   PARAFFINS.  37 

2.  The  ethyl  sulphuric  acid  reacts  with  a  second  alcohol 
molecule. 

CH..CH,     -ov  ^o  CH8.CH, 

+  H,SOt 


+  CH,  •  CH; 


H/0'      ^O  CH 


v 
>0 

8  •  CH2 


The  H2O  is  not  liberated  but  immediately  goes  to  recon- 
struct the  sulphuric  acid. 

This  is  an  example  of  catalysis  where  the  active  agent  in  a 
reaction  is  not  itself  affected  except  perhaps  temporarily  as  in 
this  instance  (p.  10). 

Theoretically  therefore  a  given  amount  of  H2SO4  should  be 
able  to  convert  an  unlimited  amount  of  alcohol  into  ether.  But 
owing  to  secondary  reactions  the  H2SO4  is  in  practice  gradually 
exhausted. 

The  esters  are  the  result  of  a  reaction  between  the  OH  group 
of  an  alcohol  and  the  OH  group  of  an  acid  with  loss  of  water, 
i.  e.j  of  an  organic  base  with  an  acid. 

Example. 

Ethanoi.  CH8 .  CHa  I  OH  CH3  -  OT, 

+  )>0      +  H20 

Ethan  acid.  CH3  •  COO  |  H  CH3  •  CO 

Ethanacetester. 

As  with  the  ethers  the  alcohols  and  acids  are  not  necessarily 
corresponding  homologues,  so  that  one  can  have  methylacet- 
ester,  ethylpropanacidester,  etc. 

The  acid  may  be  mineral  as  well  as  organic. 

CH,  •  CH2 
CH3.CH2|OH         =  \0     +H20 

Nitric  acid.  O2N— O  j  H  O2N 

Ethyl  nitrate. 


38  OUTLINES    OF   PHYSIOLOGICAL   CHEMISTRY. 

The  Anhydrids  are  formed  by  reaction   between  the  OH 
groups  of  two  acids  with  loss  of  water  : 
Example. 

Acetic  acid.  CHS'  COO  j  H  CH3'  CO 

Acetic  acid.  CHS-  CO1- OH  /°       +H'° 

CH3-  CO 

Acetanhydrid. 

The  ethers,  esters  and  anhydrids  may  therefore  be  shown  in 
diagrammatic  form  as  follows  : 

Alcohol v  Alcohol v  Acid v 

Alcohol /  Acid       /  Acid / 

Ether.  Ester.  Anhydrid. 

The  gases  carbon  monoxide  C  =  O  and  carbon  dioxide 
O=C=O  may  be  regarded  as  anhydrids,  since  they  may  be 
obtained  by  driving  off  water  from  formic  and  carbonic  acids. 


r20    =    H-O-C-H 


O=O-}-H2O     =     H— O— C— H  Formic  acid. 

O=C=0+H2O     =     H— 0— C-O-H  Carbonic  acid. 

It  has  been  said  that  the  C  atom  cannot  support  more  than 
one  OH  group.  This  is  true  as  a  general  rule  but  an  exception 
must  be  made  in  the  case  of  carbonic  acid.  Carbonic  acid  how- 
ever only  exists  as  such  in  solution  in  water,  and  is  easily 
decomposed,  CO2  gas  being  driven  off.  It  is  therefore  unstable 
having  a  tendency  to  throw  off  H2O  on  the  slightest  provoca- 
tion. Its  salts  however  are  stable,  e.  g.,  K2CO3 ;  CaCO3. 

It  has  also  been  said  that  every  C  atom  must  have  all  four 
valences  occupied.  Carbon  monoxide  is  the  single  exception  to 
this.  It  is  formed  on  combustion  with  insufficient  supply  of 
oxygen. 


OXIDATION  PRODUCTS  OF  THE  PARAFFINS.  39 

DIATOMIC  ALCOHOLS. 

A  second  group  of  a  chain  may  become  oxidized,  so  that  two 
OH  groups  are  present  instead  of  one. 

CH8  CH2OH  CH2OH 

CHS  CH3  CH,OH 

thanol  (alcohol),  Ethandiol 

monoatomic.  diatoi 


Ethane.  Ethanol  (alcohol),  Ethandiol  (glycol), 

"     >mic. 


Of  these  two  OH  groups  one  may  become  further  oxidized  to 
an  acid,  forming  an  oxyacid,  and  again  both  groups  may  become 
oxidized  to  form  a  diacid.  The  intermediate  aldehydes  need 
not  be  considered  in  detail. 

CH2OH  COOH  COOH 

CH2OH  CH2OH  COOH 

Ethandiol  (glycol).  Ethanoxyacid,  Ethandiacid, 

(oxyacetic  acid),  (oxalic  acid), 

monobasic  acid.  dibasic  acid. 

In  the  same  way  we  may  have  propandiol  and  diacid,  or 
butandiol  and  diacid,  etc.,  propanoxyacid  and  so  on.  Graphic 
formulas  of  these  and  many  others  should  be  constructed  in 
order  to  fully  grasp  the  situation. 

TRIATOMIC  ALCOHOLS. 
There, may  be  three  groups  oxidized  to  OH  and  in  this  case 

we  have  a  triatomic  alcohol. 

CH2OH 

CHOH 

CH2OH 

Propantriol  (glycerin  or  glycerol). 

In  like  manner  alcohols  may  be  tetratomic,  pentatomic,  etc. 
Mannite  is  an  alcohol  with  six  C  atoms  all  of  which  are  oxi- 
dized to  OH.  It  is  therefore  a  hexatomic  alcohol. 


40  OUTLINES   OP   PHYSIOLOGICAL   CHEMISTRY. 

It  is  obvious  that  in  the  case  of  a  diacid  the  acid  radicals 
must  be  at  either  end  of  the  chain  since  an  acid  radicle  requires 
three  valences  =  O  and  —  OH,  whilst  two  only  are  available 
in  the  middle  C  atoms,  but  with  the  oxyacids  the  alcohol  OH 
may  be  attached  to  any  of  the  C  atoms.  According  to  the 
position  of  the  alcohol  OH  group  with  regard  to  the  acid  group 
the  oxyacid  is  called  alpha,  beta,  gamma,  etc. 


yCH3  yCH3  yCH2OH 

Butanacid  a  oxybutanacid  0  oxybutan  y  oxybutan 

(butyric  acid),    (a  oxybutyric  acid).          (butyric)  acid.  (butyric)  acid. 


Lactic  Acid  is  oxypropanacid  and  it  is  evident  that  the  OH 
group  may  hold  either  one  of  two  positions. 

COOH 
HCOH 

CH3  CH2OH 

0  oxypropanaci 
(ethylene  lactic  acid). 


a  oxypropanacid  |8  oxypropanacid 

(ethylidene  lactic  acid). 


ASYMMETRIC  CARBON  ATOM  AND  ITS  ACTION  ON 
POLARIZED  LIGHT. 

Taking  the  middle  C  of  the  a  oxypropanacid  we  find  that 
there  are  four  different  groups  of  atoms  attached  to  it,  COOH, 
CH3,  H  and  OH,  whilst  the  middle  C  of  the  ft  acid  has  only 
three  different  kinds  attached,  COOH,  CH2OH  and  H. 

The  former  is  an  asymmetric  C  atom  and  the  latter  a  sym- 
metric C  atom.  Any  C  atom  to  which  2,  3,  or  4  similar  atoms 
or  groups  of  atoms  are  attached  is  symmetric.  Any  C  atom 
which  has  four  different  groups  attached  to  it  is  asymmetrical. 

If  the   molecule   is   regarded   as  existing  in  three  planes 


OXIDATION   PRODUCTS    OF   THE    PARAFFINS. 


41 


(stereo-chemistry),  as  no  doubt  is  the  case  in  nature,  we  can 
construct  a  diagram  of  it  as  follows  : 


1.  Asymmetric.  3.  Symmetric. 

If  the  attached  groups  are  arranged  in  a  different  order  as 


2.  Asymmetric. 


4.  Symmetric. 


it  will  be  found  that  molecule  No.  1  cannot  be  placed  directly 
over  molecule  No.  2  in  such  a  way  that  each  group  lies  over  a 
corresponding  group.  But  if  the  molecules  are  turned  over  in 
opposite  directions,  the  groups  will  then  correspond.  One  is 
the  mirror  image  of  the  other. 


With  a  symmetric  C  atom  (3)  and  (4),  no  matter  how  the 
two  or  more  similar  groups  may  be  placed,  one  molecule  can 
always  be  superimposed  upon  another  in  such  a  way  that  each 
group  has  a  corresponding  one  underneath  it.  There  is  no 
necessity  to  turn  the  molecules  over. 


42  OUTLINES   OF  PHYSIOLOGICAL  CHEMISTRY. 

With  an  asymmetric  C  atom  no  matter  how  the  groups  are 
arranged  one  molecule  can  always  be  made  to  fit  on  another, 
provided  they  are  turned  over  as  shown  in  the  diagram. 

If  a  small  model  is  made  with  wire  and  differently  colored 
balls  this  fact  is  made  obvious  at  a  glance. 

With  an  asymmetric  C  atom  then  there  are  always  two  dif- 
ferent combinations  possible,  but  no  more. 

One  of  these  combinations  when  in  solution  always  has  the 
power  of  turning  the  plane  of  polarized  light  to  the  right  (dex- 
trorotatory) and  the  other  to  the  left  (Isevorotatory).  Why  this 
is  so  is  not  clearly  understood ;  the  fact  has  to  be  accepted. 

When  an  equal  number  of  such  right-  and  left-handed 
molecules  are  in  solution  together,  they  neutralize  each  other 
and  the  solution  has  no  power  over  polarized  light.  It  is  the 
inactive  or  racemic  form  of  the  compound. 

Alpha  lactic  acid  may  exist  in  three  different  forms,  all  of 
which  give  similar  reactions,  except  that  one  is  dextrorotatory 
(d)  another  Isevorotatory  (I)  and  the  third  inactive  («'),  whilst 
ft  lactic  acid  exists  in  one  form  only. 

The  a  and  /3  lactic  acid  are  chemical  isomers.  The  differ- 
ences in  their  make-up  are  due  to  different  chemical  combina- 
tions. The  differences  between  d  and  I  lactic  acid  are  simply 
differences  of  configuration.  They  are  physical  or  space 
isomers. 

Following  up  the  question  of  the  asymmetric  carbon  atom 
we  may  consider  a,  @  dioxybutyric  acid 

COOH .  CHOH .  CHOH .  CH3 

and  constructing  its  graphic  stereochemical  formula  in  three 
planes,  find  that  it  has  two  asymmetric  C  atoms. 

No  single  one  of  these  can  be  so  placed  over  another  that  all 
the  groups  correspond,  but  if  1  and  2  are  turned  so  as  to  face 


OXIDATION   PRODUCTS   OF   THE   PARAFFINS.  43 

each  other  their  groups  correspond.     1  is  the  mirror  image  of 
2,  and  the  same  is  the  case  with  3  and  4. 

There  are  therefore  two  right-handed,  two  left-handed  and 
two  racemic  forms,  or  we  may  say  there  are  four  space  isomers. 


)H 
1234 

Tartaric  add  is  butandioldiacid, 

COOH .  CHOH .  CHOH .  COOH. 

So  this  also  has  two  asymmetric  C  atoms,  but  in  this  case  each 
of  the  two  central  C  atoms  has  similar  groups  attached, 
COOH,  OH  and  H. 


Taking  1  and  2  we  find  that  the  groups  A  attached  to  the 
upper  C  atom  do  not  correspond  with  the  groups  E  attached  to 
the  lower  C  atom.  Nor  do  the  groups  A  form  a  mirror  image 
of  the  groups  E.  But  the  entire  molecule  1  forms  a  mirror 


44  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

image  with  the  entire  molecule  2.  1  and  2  are  dextro  (d)  and 
laevorotatory  (I)  respectively,  and  together  are  inactive  or  racemic. 

On  studying  3  however  we  find  that  the  groups  A  are  the 
mirror  image  of  the  groups  J5.  These  two  therefore  neutralize 
each  other  by  what  is  called  internal  compensation  and  the 
molecule  in  solution  is  inactive.  The  same  is  the  case  with  4, 
and  since  each  of  these  is  of  itself  inactive  a  mixture  of  the  two 
is  also  inactive.  3  and  4,  either  singly  or  mixed,  form  only 
one  single  inactive  compound,  mesotartaric  acid. 

Tartaric  acid  therefore  has  three  space  isomers  or  four  forms 
instead  of  six  as  with  /?  dioxybutyric  acid.  The  latter  is  said 
to  be  an  asymmetric  molecule  whilst  tartaric  acid  is  a  symmetric 
molecule. 

The  dextrorotatory  may  be  separated  from  the  Isevorotatory 
form  in  a  racemic  solution  of  tartaric  acid  : 

1.  By  sorting   the  crystals  which   are  formed   with  some 
optically  inactive  substance.     The  d  crystal  has  a  slightly  dif- 
ferent form  from  the  I  crystal ;  one  being  a  mirror  image  of  the 
other. 

2.  By  the  different  solubilities  of  certain  salts  of  the  two 
forms.     The  strychnine  salt  is  commonly  used. 

3.  Certain  moulds,  e.  g.,  penicillium  glaucum,  if  grown  on  a 
racemic  solution,  feeds  on  the  d  form  and  destroys  it,  leaving  the 
I  form  untouched. 

Fats.  —  Three  of  the  higher  monobasic  (fatty)  acids  are  of 
special  interest  in  this  connection  and  may  be  referred  to  here : 
They  are ; 


COOH  COOH 


CH,  CH8 

Palmitic  acid,  C16H^O^      Stearic  acid.  C^HMOV      Oleic  acid.  C^H^C 


OXIDATION   PRODUCTS   OF   THE   PARAFFINS.  45 

Oleic  acid  differs  slightly  frcm  the  other  two  in  that  it  con- 
tains two  unsaturated  carbon  atoms  C  =  C. 

The  esters  of  these  acids  with  the  triatomic  alcohol  glycerin 
are  the  ordinary  fats  of  the  body.  The  combination  occurs  as 
follows  : 


H»9"~Gd5    H|— O— 0).(CH2)ie.CH3     H2C-0-CX>(CH2)16.CH, 
HV~  $EK  ^H|-0-CO.(CH2)16.CH3  =  HC-O.CO.(CH2)16.CHS+3H20 
H2C—  lo—H.    Hi— O— Ca  (CH3)16-CH3     H2C— O— CO- (CH3)16-CH8 


Glycerin    -f    3  Btearic  acid,  =  Tristearin      -f    3  water. 

CSH6(OH)3  +  3HSt.  =  CaHsSt3         +  3H2O. 

Tripalmitin  and  triolein  are  formed  in  the  same  way.  The 
fats  of  the  animal  body  are  composed  of  these  three  substances 
mixed  in  varying  proportions.  The  greater  the  proportion  of 
olein  the  lower  the  melting  point  of  the  fat. 

Unsaturated  compounds  have  a  lower  melting  point  than  their 
corresponding  saturated  compounds.  Olein  therefore  is  a  fluid 
at  ordinary  temperature  whilst  stearin  and  palmitin  are  solids. 

Soaps.  —  Free  fatty  acid  treated  with  an  alkali  or  alkaline 
base  will  combine  with  it  to  form  a  soap. 

Example. 

COOK 

16  +  KOH  =  (CH2)18  -f  H20 

f^TT 

^-f-3 

Potassium  stearate  (a  soap). 

Soaps  are  compounds  formed  by  replacing  the  hydrogen  of  a 
fatty  acid  by  a  metal.  Soaps  of  the  alkali  metals  are  soluble 
in  water.  Others,  calcium  soap,  lead  soap,  etc.,  are  insoluble. 

On  boiling  fat  with  an  alkali  the  latter  will  drive  off  the 
glycerin  and  form  a  soap  (saponification) 

C3H5St3    +    3KOH    =    3KSt    -f    C3H5(OH)3. 

Stearin      -f      Pot.  hydroxide  =  Pot.  stearate      +       Glycerin. 


46 


OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 


It  is  worth  while  to  distinguish  between  the  fats  and  the 
waxes. 

The  fats  are  the  esters  of  glycerin  and  a  higher  monobasic  acid. 

The  waxes  are  the  esters  of  a  higher  monobasic  alcohol  and 
a  higher  monobasic  acid. 

Or  diagram  matically, 


Triatomic  alcohol 
(glycerin). 


3  (Higher  fatty  acid). 


Higher  monoatomic  alcohol 
up  to  C30. 

Higher  fatty  acid 
up  to  C18. 


Fats.  Waxes. 

The  fats  and  oils  are  chemically  alike.     A  fat  when  melted 
is  called  an  oil,  and  a  solidified  oil  a  fat. 

The  true  oils  have  of  course  nothing  in 

A  common  with  the  mineral   oils  which  are 

hydrocarbons   and  should,   properly  speak- 
ing, be  called  paraffins. 


A  .Ether- 
B    TVater 


FlG.  4. 


TESTS  FOR  FATS. 
A.  Staining  reactions. 

1.  Sudan  III.  is  a  red  stain  which  colors 
all  fats  but  no  other  substances.     It  is  in- 
soluble in  water,  so  has  to  be  used  in  alco- 
holic solution. 

2.  Osmic  acid  stains  olein  black,  but  does 
not   affect   other   fats.     Since   animal   fats 
always  contain  more  or  less  olein,  osmic  acid 
is  useful  for  their  demonstration,  although 
for  general  purposes  is  not  so  reliable  as 
Sudan  III.     It  is  generally  used  in  1  per 


cent,  aqueous  solution. 


OXIDATION   PRODUCTS   OF   THE    PARAFFINS.  47 

B.  Ether.  —  The  fats  and  free  fatty  acids  (not  the  soaps)  are 
soluble  in  ether,  so  that  this  is  much  used  as  a  means  of  extract- 
ing fats.  The  tissue  or  whatever  else  it  may  be,  is  shaken  well 
with  ether  in  a  test-tube  —  there  are  many  forms  of  apparatus 
for  doing  this  on  a  large  scale  and  more  thoroughly  —  and  the 
ether  then  separated  from  the  other  material  in  a  separating 
funnel  (Fig.  Jf) ;  the  ether  containing  the  fat  in  solution  rises  to 
the  top. 

The  ether  is  collected  in  a  porcelain  dish,  allowed  to  evap- 
orate and  the  residue  tested  for  fats,  by  staining  and  other 
reactions  which  need  not  be  mentioned  here. 

CARBOHYDRATES. 


Carbohydrates. 

Mono- 
saccharides 
(simple  sugars). 

Disaccharides 
(compound  sugars). 

Poly- 
saccharides 
(starches). 

The  carbohydrates  are  normal  chains  of  C  atoms  containing 
H  and  O  in  the  proportion  of  water. 

Empirical  formula  of  a  carbohydrate  CnH2j.Ox. 

1.  Monosaccharides.  —  The  sugars  are  aldehydes  or  ketones 
with  the  remaining  C  atoms  in  the  chain  oxidized  to  alcohol  (OH). 

For  convenience  the  sugars  are  all  called  by  names  ending  in 
ose  with  a  prefix  indicating  the  number  of  C  atoms. 

The  simplest  possible  sugar  is  a  biose. 


O=CH 
H,COH  HCOH 

H3COH  H2COH 

Biose.  Triose  (aldose).  Triose  (ketose). 

and  so  on,  tetrose,  pentose,  hexose,  etc. 


48 


OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 


The  only  monosaccharides  which  occur  in  nature  are  certain 
pentoses  and  hexoses,  of  which  the  following  are  the  best  known. 

HC=O  HC=0 

)HOH  CHOH 

IEOH  CHOH 

}HOH  CHOH 

,OH  CHOH 


Xylose  (pentose-aldose). 


CHZOH: 

Glucose  (hexose-aldose). 


CH2OH 

C=O 

CHOH 

CHOH 

CHOH 


CH2OH 

Fructose  (hexose-ketose). 


The  monosaccharides  occurring  in  nature  have  all  been  syn- 
thesized in  the  laboratory  and  in  addition  to  these  a  number  of 
other  pentoses  and  hexoses,  besides  trioses,  tetroses,  heptoses, 
octoses  and  nonoses. 

About  12  natural  sugars  are  known  and  over  50  have  been 
synthesized. 

A  glance  at  the  graphic  formula  of  a  sugar  will  show  that 
there  are  a  large  number  of  asymmetrical  C  atoms,  and  the 
number  of  possible  combinations  amounts  to  16  with  the  hexal- 
doses  and  8  with  the  hexketoses. 

There  are  therefore  24  possible  optically  active  hexoses 
besides  the  racemic  forms.  This  can  be  easily  verified  by  con- 
structing graphic  formulas,  and  it  is  worth  while  to  do  it. 

The  aldoses  can  be  oxidized  to  acids.  From  glucose  for 
instance  three  acids  can  be  obtained. 


Glyconic  acid. 


)H 

Saccharic  acid. 


)H 

Glycuronic  acid. 


OXIDATION   PRODUCTS   OF   THE   PARAFFINS.  49 

Gly  conic  and  glycuronic  acid  being,  like  the  aldoses,  asym- 
metric molecules  with  four  asymmetric  C  atoms,  each  have  16 
optical  modifications.  But  saccharic  acid  is  a  symmetric  mole- 
cule, so  some  of  its  forms  are  meso. 

The  meso  forms  are  : 


and  the  three  forms  which  are  the  reverse  of  these,  so  there  are 
three  meso  forms  and  ten  optically  active  forms,  13  space 
isomers. 

If  glucose  is  oxidized  in  the  laboratory  the  aldehyde  group 
is  first  acted  upon  and  gly conic  acid  is  obtained.  Further  oxi- 
dation affects  the  alcohol  group  at  the  other  end  and  saccharic 
acid  is  produced.  The  chain  cannot  be  oxidized  beyond  this 
stage  without  breaking  up. 

In  the  body  the  aldehyde  group  appears  to  be  protected  in 
some  way,  so  that  the  alcohol  group  at  the  other  end  is  first 
oxidized  and  glycuronic  acid  is  formed.  On  further  oxidation 
in  the  body  glycuronic  acid  breaks  up.  Glycuronic  acid  ap- 
pears in  the  urine  under  conditions  which  will  be  explained 
later  on. 

The  aldoses  by  virtue  of  their  aldehyde  group  will  reduce 
copper  oxide  (Fehling)  as  already  described  for  aldehydes.  It 
was  said  that  this  is  an  aldehyde  and  not  a  ketone  reaction  but 
a  ketone  containing  a  number  of  alcohol  groups  will  react,  so 
that  the  ketoses  will  reduce  copper  oxide  or  bismuth  oxide  as 
well  as  the  aldoses. 
4 


50 


OUTLINES   OF    PHYSIOLOGICAL   CHEMISTRY. 


Other  sugar  reactions  will  be  discussed  in  Chapter  V. 

2.  Disaccharides.  —  A  disaccharide  is  a  combination  of  two 
sugars  with  loss  of  H2O.  The  empirical  formula  of  a  monosac- 
charide  being  C6H12O6,  that  of  a  disaccharide  is  C12H22On. 

The  more  important  disaccharides  are  : 

Saccharose  which  is  glucose  -f  fructose, 
Maltose  which  is  glucose  -f  glucose, 
Lactose  which  is  glucose  -f-  galactose. 

Maltose  and  lactose  will  reduce  Fehling's  solution  but  saccha- 
rose (cane  sugar)  will  not. 

The  reason  for  this  is  that  the  latter  is  so  constructed  that 
the  aldehyde  group  of  the  glucose  and  the  ketone  group  of  the 
fructose  both  enter  into  the  combination,  whilst  with  the  two 
former  one  aldehyde  group  is  left  free  in  each  case. 

To  illustrate  this  the  construction  of  saccharose  and  maltose 


is  given, 


(A) 

HC=0 

CHOH 
CHOH 

EOH 
OH 
, 
(A) 

Maltose,  one  free  aldehyde  group. 


CH2OH 
CHOH 

HC 0- 

CHOH 
[OH 


OH 


OH 


Saccharose,  no  free  aldehyde  or  ketone  group. 


The  aldehyde  and  ketone  groups  are  marked  A  and  K. 

3.  Polysaccharides.  —  A  number  of  monosaccharide  or  disac- 
charide molecules  may  be  combined  together  to  form  polysac- 
charides  and  each  time  a  fresh  monosaccharide  or  disaccharide 
is  added  there  is  loss  of  H2O  so  that  the  empirical  formula  of 
a  polysaccharide  is  (C6H10O5)n.  The  polysaccharides  are  very 


OXIDATION   PRODUCTS   OF   THE    PARAFFINS.  51 

complex  bodies  and  the  number  of  sugar  molecules  which  they 
contain  is  not  known. 

The  principal  polysaccharides  are : 

1.  Cellulose.     Fibrous  and  woody  parts  of  plants. 

2.  Starch.     Keserve  material  in  seeds,  roots  and  other  parts 
of  plants. 

3.  Glycogen  or  animal  starch. 

4.  Dextrins.     Bodies  intermediate  between  any  of  these  three 
and  sugars. 

Reactions  of  polysaccharides  with  iodine  (LugoFs  solution). 

Starch  gives  a  blue  color. 

Glycogen  gives  a  reddish  brown  color. 

Dextrins  (a)  a  red  color  (erythrodextrin). 
(6)  no  color  (leucodextrin). 

The  di-  and  poly-saccharides  on  boiling  with  dilute  mineral 
acids,  H2SO4  is  generally  used,  are  decomposed  into  monosaccha- 
rides  by  a  process  of  hydrolysis.  The  acid  acts  as  a  catalyzer. 

Hydrolysis  is  the  breaking  down  of  complex  into  simpler 
molecules  with  addition  of  water. 

I — i 


=    ' 1— O-H  +  H- 


-f-HJOH 

It  must  have  been  already  noticed  that  H2O  plays  a  con- 
spicuous part  in  reactions. 

Two  molecules  may  condense  into  one  with  loss  of  H2O  — 
"  Dehydration."  One  molecule  may  split  into  two  with  addi- 
tion of  H2O  —  "  Hydration  "  or  "  Hydrolysis." 

On  building  up  the  starch  molecule  from  a  monosaccharide 
there  is  dehydration,  and  on  breaking  it  down  into  its  com- 
ponent monosaccharides  there  is  hydrolysis. 

Cane  sugar  on  boiling  with  acids  is  hydrolyzed  to  glucose 
and  fructose. 


52 


OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 


The  more  complex  insoluble  starch  molecule  is  hydrolyzed  by 
a  succession  of  steps  through  the  dextrins  and  the  disaccharide 
maltose,  to  glucose.  The  process  is  precisely  similar  to  that 
which  is  carried  out  by  the  enzymes  or  ferments,  amylase,  and 
maltase,  and  is  discussed  more  fully  in  Chapter  VII. 

HYDROLYSIS  AND  SAPONIFICATION. 

We  may  digress  a  little  here  to  point  out  the  differences 
between  hydrolysis  and  saponification.  The  terms  are  only 
used  for  reactions  with  organic  compounds. 

Hydrolysis  is  simplification  with  absorption  of  water. 

Saponification  is  simplification  with  absorption  of  a  hydroxide. 

Hydrolysis  may  take  place  at  the  point  of  junction  between 
any  two  molecules  forming  a  complex,  whether  alike  or  not, 
whether  acid,  basic  or  neutral,  since  the  agent  of  hydrolysis, 
H2O,  is  neutral. 

Saponification  can  only  take  place  when  one  of  the  molecules 
forming  the  complex  is  an  organic  acid,  since  the  agent  of 
saponification  KOH  or  other  hydroxide,  is  a  base  and  can  only 
react  with  an  acid. 


1. 


Examples  of  hydrolysis. 

Glycerin  / 

radical     ~O-St.  +  3H3O 

\)-St. 

glycerin  -f  3  (stearic  acid). 


Examples  of  saponification. 

O-St. 


Fat 


o       Glucose — O — glucose   ,    TT  s\ 
*       radical  radical  "*  **** 

Maltose  =  glucose  +  glucose. 

CH3.qp 

3.  \>  +  H20 
CH3-CH2 

(Ethylacetester)  =  CHS  •  COOH  +  CH3  •  CHaOH, 
(acetic  acid  +  alcohol). 

PITT       C*T1 
v^il3  •  v>XZ2 

4.  ;0  +  H20 
CH3  •  CH2 

Ethylether  =  CH3  •  CHaOH  +  CH3  •  CHaOH. 


r  O-St. 

=  glycerin  +  3  (potassium  stearate,  a  soap). 

glucose—  O—  glucose   , 
Mri^oi  ~o,i;«oi  "T 


radical  radical 

s=  no  reaction. 

CH,.qo 

^>0  +  KOH 
CH3  •  CH2 

=  CH3  •  COOK  +  CH3  •  CH2OH, 
(potassium  acetate  +  alcohol). 

CH3  •  CH2 

">0  +  KOH 

CH3  •  CH2 

=  no  reaction. 


OXIDATION   PRODUCTS    OF   THE    PARAFFINS.  53 

Other  hydroxides,  NaOH,  C&(OH)V  Ba(OH)2,  etc.,  saponify 
equally  well.  We  may  have  calcium  soaps,  lead  soaps  and  so 
on.  Any  esters  can  be  saponified  (example  3)  although  the 
resulting  compound  may  not  be  what  we  commonly  regard  as 
a  soap. 

The  terms  however  are  somewhat  loosely  used.  The  organic 
chemist  seldom  makes  any  distinction  between  hydrolysis  and 
saponification,  the  latter  term  being  often  used  to  describe  a 
process  which  is  in  reality  hydrolysis.  For  instance  the 
"  saponification  "  of  fats  by  superheated  steam,  or  of  an  ester  by 
the  action  of  an  acid.  In  each  case  an  acid,  not  a  salt,  is  one 
of  the  products,  so  that  strictly  speaking  this  is  hydrolysis. 


CHAPTER  IV. 

A.    HALOGEN  DERIVATIVES  OF  CARBON  COMPOUNDS. 

IF  CH4  is  treated  with  chlorine  gas  it  displaces  one  or  more 
of  the  H  atoms,  according  to  the  amount  of  chlorine  used. 

H  H  H  Cl  Cl 

I  I  I  I  I 

H-C-H      H-C-C1     H-C-C1     H-C-C1     C1-C-C1 

I  I  I  I  I 

H  H  Cl  Cl  Cl 

Methane.         Monochlor-  Dichlor-  Trichlor-          Tetrachlor- 

methane.  methane.  methane  methane, 

(chloroform). 

Similar  compounds  are  formed  with  bromine  and  iodine. 
Chloroform  is  trichlormethane         CHC13, 
lodoform  is  triodomethane  CHI3, 

Bromoform  is  tribromethane  CHBr3. 

lodoform  can  be  made  from  alcohol  on  addition  to  the  latter 
of  a  solution  of  iodine  in  NaOH  and  heating. 

C2H6OH  +  6NaOH  +  4I2  =  CHIS+  HCOONa  +  5NaI  +  5H2O 
This  reaction  is  used  as  a  test  for  alcohol  in  solution,  the 
merest  trace  of  iodoform  being  perceptible  by  its  odor.     If 
alcohol  is  present  in  appreciable  quantities  iodoform  separates 
out  as  a  yellow  precipitate. 

B.    SULPHUR  COMPOUNDS. 

S  and  O  are'  interchangeable  in  a  variety  of  compounds. 
The  interchange  %may  take  place  in  the  alcohol  (OH)  groups  of 
oxidized  carbon  compounds  with  formation  of  mercaptans. 
H2COH  H2CSH 


+  H20 
CH3  CH3 

Ethanol.  Thioethanol  (ethylmercaptan). 

54 


NITROGEN   COMPOUNDS.  55 

Methyl,  propyl,  etc.,  mercaptans  can  be  formed  in  the  same 
way.  The  mercaptans  are  recognizable  by  their  garlic  odor, 
and  the  above  reaction  may  be  used  as  a  test  for  alcohols. 
Direct  H2S  however  cannot  be  used.  The  reaction  is  obtained 
indirectly  as  follows : 

5C2H5OH  +  P2S5  =  5C2H5SH  +  P,O6. 

C.    NITROGEN  COMPOUNDS. 

The  protoplasm  of  the  living  body  yields  fats,  carbohydrates 
and  proteids.  The  fat  and  carbohydrate  molecules,  already 
discussed,  contain  no  N,  but  all  proteids,  their  modifications 
and  derivatives  contain  it,  so  that  a  consideration  of  the  com- 
binations of  nitrogen  and  carbon  is  in  fact  an  introduction  to 
the  study  of  proteids,  and  therefore  of  special  importance  to  the 
physiological  chemist. 

Nitrogen  (N)  has  three  or  five  valences.  In  the  latter  case 
one  of  the  attached  groups  is  usually  OH,  or  represents  OH. 

N  =  H3  H-0-N  =  H4  C1-N=H4. 

Ammonia.  Ammonium  hydroxide.  Ammonium  chloride. 

INTRODUCTORY. 

Carbon  dioxide  gas,  CO2,  in  solution  takes  up  H2O  to  form 
carbonic  acid,  CO(OH)2. 

Ammonia,  NH3,  in  solution  takes  up  H2O  to  form  ammonium 
hydroxide,  NH4OH. 

Carbonic  acid  and  ammonium  hydroxide  will  combine 
together  to  form  ammonium  carbonate  and  water. 

H— O— C— O— NH4  H4N— O— C— O— NH4 

Monoammonic  carbonate.  Diammonic  carbonate. 


56  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTKY. 

The  OH  of  monoammonic  carbonate  may  be  replaced  by 
other  groups,  a  chain  of  C  atoms  for  instance,  and  the  formula 
may  be  written  as 


K— C— O— NIL 


B,  being  any  organic  radical.     Suppose  R  is  CH3,  we  then  have 
CH3  —  COONH4  or  ammonium  acetate. 

This  may  also  be  called  methylammonium  carbonate. 

If  R,  —  COONH4  is  deprived  of  H2O  we  have 


JL 


-NH2 
an  amid. 
If 


R— C— NH, 


is  deprived  of  H2O  we  have  R— C= N  a  nitril  or  cyan  compound. 
The  difference  between  nitrils,  amids,  and  ammonium  car- 
bonate is  merely  a  matter  of  less  or  more  water  in  combination, 
so  that  they  are  evidently  closely  related. 

NITRILS. 

Hydrocyanic  acid        H  —  C  =  N, 
Isohydrocyanic  acid    H  —  N  =  C. 

On  oxidation : 

Cyanic  acid  H  -  O  -  C  ==  N, 

Isocyanic  acid  H  —  N  =  C  =  O, 

Examples  of  salts. 

Potassium  cyanide      K  —  C  =  N, 
Potassium  cyanate      K  —  O  —  C  =  N. 


NITROGEN    COMPOUNDS.  57 

The  highly  poisonous  nitrils  or  cyan  compounds  readily  take 
up  sulphur,  forming  with  it  harmless  so-called  rhodanid  com- 
pounds, or  more  commonly  sulphocyanides. 

HCN  +  S  =  H  -  S  -  CN. 

Thiocyanic  acid. 

Thiocyanic  acid  itself  is  somewhat  poisonous,  but  its  salts  are 
not. 

Isothiocyanic  acid  H  —  N  =  C  =  S  bears  the  same  relation 
to  isocyanic  acid  as  thiocyanic  acid  does  to  cyanic  acid.  In 
each  case  S  takes  the  place  of  O  (cf.  mercaptans). 

The  isocyan  compounds,  isomers  of  the  cyan  acids,  are  also 
called  acids  but  they  are  not  true  acids.  They  do  not  form 
stable  salts  with  bases,  but  enter  into  combination  with  certain 
other  substances  in  a  characteristic  manner.  They  will  be 
referred  to  again. 

B,  —  C  =  N  readily  attaches  itself  to  an  aldehyde  group  and 
by  this  means  sugars  have  been  synthesized.  Starting  with 
glycerin  the  following  graphic  formulas  explain  the  process  : 


HO)H 

oxidized  to       CHOH       -f    HCN    =       CHOH 
CZ2OH  CH2OH 

Triose. 


o=c—ox 

CHOH  CHOH 

+  2H20  =         CHOH  H2O  =       CHOH 

CH2OH  CH2OH 

Ammonium  butyrate  or  propantriol  Butantriol 

ammonium  carbonate.  amid. 

O=COH 

CHOH 
+    HNO2    =  CHOH 

OH  CH2Gfl 

Butantriol  amid.  Butantriol  monacid. 


58  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 


reduced  to 


H2OH 


Butantriol  monal 
Tetrose. 

A  triose  has  been  converted  into  a  tetrose,  and  by  the  same 
process  a  tetrose  can  be  converted  into  a  pentose,  a  pentose  into 
a  hexose.  Sugars  have  been  synthesized  in  this  way  up  to  a 
nonose. 

It  has  to  be  taken  for  granted  that  chemists  can  reduce, 
oxidize,  hydrate,  dehydrate,  etc.,  at  will  within  certain  limits. 
To  enter  into  details  of  the  methods  employed  would  be  out  of 
place  here. 

AMIDS,  AMINS,  AMINO  ACIDS. 

1.  Amids.  —  An  amid  is  the  result  of  a  reaction  between  the 
OH  group  of  an  acid  and  NH3. 

Example : 

0=C-NH, 

L      +H,O 

v>n.j 

Acetic  acid,  CH3-  COOH  Acetamid,  CH3-  CONHa 

2.  Amins.  —  An  amin  is  the  result  of  a  reaction  between  the 
OH  group  of  an  alcohol  and  NH3. 

Example : 


H2C-!0-H 


CH, 

Ethylalcohol,  CH3-  CH2OH  Ethylamin,  CHS-  CHaNHa 


NITROGEN   COMPOUNDS.  59 

3.  Amino  (amido)  adds.  —  An  amino  acid  is  the  result  of  a 
reaction  between  the  alcohol  (OH)  group  of  an  oxyacid  and 


NH3. 


Example  : 

ZHl 


COOH 
Oxyacetic  acid,  CH,OH-  COOH.  Aminoacetic  acid,  CH»NHt-  COOH. 

These  reactions  are  intended  merely  to  show  the  structure  of 
the  compounds  and  do  not  represent  the  methods  by  which  they 
are  formed  in  the  laboratory. 

The  prefix  am  always  denotes  an  —  KH2  group.  For  an 
=  NH  group  the  prefix  im  is  used.  Thus  we  may  have  imids 
and  imins.  How  these  arise  will  become  clear  as  we  proceed. 

1.  AMIDS. 

An  amid  may  be  formed  from  any  of  the  organic  acids. 
Example  : 

COOH  CONH, 

L,      +NH'=     Ik    +H«0 

Ethan  acid  (acetic  acid).  Ethan  amid  (acetic  amid). 

and  similarly  for  the  higher  homologues,  propanamid,  butan- 
ainid,  etc. 

But  the  most  important  for  us  is  the  diamid  urea.  Both  it 
and  the  monamid  carbamic  acid  may  be  formed  from  the 
ammonium  carbonates  with  loss  of  H2O. 

H-O-C-O—  NH4  —  H2O=  HOC—  NH, 

Monoammonic  carbonate,  H(NH4)C03.  Carbamic  acid,  HCO2NHt. 

?  ft 

H4N-O—  C-O—  NH4  —  2H2O=  H2N—  C—  NH, 

Diammonic  carbonate,  (NH4),CO3.  Carbamid  (urea),  CO(NHa),. 


60  OUTLINES  OF  PHYSIOLOGICAL   CHEMISTRY. 

Urea  was  the  first  of  the  organic  compounds  synthesized. 
Wohler  accomplished  it  in  1828  by  the  following  reaction. 


H—  N=C=O   -f    NH^OH    =    NH4—  N=C=O    +    HaO 
Isocyanic  acid    +    Ammonium  hydroxide    =    Ammonium  isocyanate. 

But  as  already  mentioned  isocyanic  acid  does  not  form  stable 
salts,  so  ammonium  isocyanate  falls  to  pieces  and  reconstructs 
itself  as  its  more  stable  isomer  urea. 

It  will  be  seen  that  the  empirical  formula  of  each  is  CH4N2O. 

BIUEET. 

1.  On  melting  crystals  of  urea  by  heating,  a  part  of  the 
molecules  condense  with  loss  of  NH3  forming  the  soluble  biuret. 

ff  -ff  fl  7 

CiraErnB  =       HaNC-N- 


= 
Urea  +  Urea.  Biuret,  CaH8NaOa. 

On  treating  a  solution  of  this  with  NaOH  and  a  very  dilute 
solution  of  CuSO4  it  gives  the  well-known  biuret  reaction,  a 
pink  to  violet  color. 

Proteid  material  gives  the  biuret  reaction,  although  proteid 
contains  no  biuret.  It  contains  however  a  radical  which  is  so 
closely  allied  to  biuret  that  it  affords  the  same  reaction,  but 
this  will  be  discussed  more  in  detail  later  on. 

2.  Another  part  of  the  urea  molecules  condense  still  further 
to  an  insoluble  compound,  cyanuric  acid. 


*  I  \  -^.-rrr 

NH 


[  H  —  N-C/" 

—    5 


X) 

-< 

Mffi 


NITROGEN  COMPOUNDS.  61 

The  latter  compound  is  unstable  and  rearranges  itself  as 

7TH 

Ho<f     ft 

N=(X)H 
Cyanuric  acid. 

Guanidin  is 


and  this  can  be  changed  to  urea  by  boiling  with  baryta  water. 

HNC(NH2),    +    H,0    =    CO(NH,)3    +    NH3 
Guanidin.  Urea. 

The  NH  is  driven  out  and  replaced  by  O. 

Since  guanidin  exists  in  combination  in  the  proteid  molecule, 
a  part  of  the  urea  excreted  is  no  doubt  formed  by  some  such 
reaction  as  this.  But  the  amount  of  guanidin  in  proteid  is  in- 
significant and  only  accounts  for  a  very  small  part  of  the  urea 
actually  excreted.  The  theories  of  urea  production  will  be 
discussed  later  on. 

AMID  N. 

In  reading  articles  on  physiological  chemistry  one  often  meets 
with  the  expression  Amid  NOT  Ammonia  N.  The  NH2  group 
of  an  amid  can  be  split  off  as  NH3  on  boiling  with  NaOH  or 
some  other  alkaline  base.  The  stronger  base  drives  out  the 
weaker  base  NH2  from  the  acid  radical. 

CO(NH2)2  +  2NaOH  =  Na2CO3  +  2NH3. 

Urea.  Sodium  carbonate. 

The  NH2  groups  of  the  amins  and  amido  acids  replace  an 
alcohol  OH  group  with  which  an  alkaline  base  has  no  affinity, 
so  they  are  not  driven  off  in  this  way  and  the  nitrogen  so  com- 


62  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

bined  is  c&lled'stable  N.  It  cannot  be  obtained  directly  as 
The  whole  molecule  must  be  broken  down  by  drastic  methods, 
by  the  use,  for  example,  of  con.  H2SO4  and  KHSO4,  and  the 
N  obtained  as  an  ammonium  salt.  This  is  the  basis  of  the 
Kjeldahl  method  of  determining  N  content. 

The  group  NH3  although  basic  seems  to  have  affinities  for 
OH  groups  apart  from  its  basic  qualities.  When  it  exists  in 
solution  as  NH4OH  it  acts  as  a  base  only.  Thus  we  can  have 

H2CNH2 
CH3 

but  not 

HaC— 0-NH4 

CH8 

THE  AMINS. 

As  a  result  of  the  action  between  the  OH  of  an  alcohol  and 
NH3  the  O  is  lost. 

K  -  COH  +  NH3  =  R  -  CNH2  +  H2O. 

So  that  the  amins  appear  as  paraffin  chains  with  NH2 
attached. 

Two,  three  or  more  NH2  groups  may  be  attached  to  a  chain 

and  in  this  case  the  compounds  are  called  diamins,  triamins,  etc. 

H2CNH3  H2CNH3 

CH8  H2CNH2 


Ethanmonamin  Ethandiamin  (ethylendiamin)  Butantriamin, 

(ethylamin).  or  dimethyleiidiamin.          (butylentriamin)  or  tetra- 

methylentriamin. 

Again  a  second  H  of  NH3  may  combine  with  another  chain, 
forming  a  secondary  amin.  If  all  three  hydrogen  atoms  of  the 
NH3  are  displaced  the  compound  is  a  tertiary  amin. 


NITROGEN   COMPOUNDS.  63 


CH3-CH3NHt  NH 

CH3  •  CH2  CH3  ' 

Primary  (ethylamin).       Secondary  (diethylarain).          Tertiary  (triethylamin). 

Any  of  the  alcohols  may  combine  with  NH3  so  that  we  may 
have  for  example,  methyl  or  propylamin,  etc.,  among  the 
primary  ;  methylethylamin,  ethylpropylamin,  etc.,  among  the 
secondary  ;  dimethylethylamin,  trimethylamin,  etc.,  among  the 
tertiary  amins. 

REACTIONS  OF  THE  AMINS. 

1.  Carbylamin  (Hofmeister's). 

Treated  with  chloroform  (CHC13)  and  alcoholic  KOH,  the 
primary  (NH2)  amins  undergo  a  peculiar  change  : 

H2CNH2+CHCl3+3KOH=3KCl+3H2O+HaC—  N=C 
CH3  CH3 

Ethylamin.  Ethylcarbylamin. 

The  K  combines  with  the  01.  This  liberates  three  OH 
radicals  (hydroxyls)  which  seize  the  remaining  H  from  the  C 
of  the  chloroform,  and  the  H2  from  the  N  of  the  amin,  to  form 
3H2O.  The  N  and  the  C  are  thus  left  unsatisfied,  so  the  C 
immediately  combines  with  the  N,  which  in  a  most  accommo- 
dating manner  increases  its  atomicity  from  3  to  5,  allowing  the 
C  to  saturate  itself  with  the  four  spare  valences. 

The  carbylamins  are  recognizable  by  their  nauseating  odor 
which  once  smelt  is  never  forgotten. 

2.  Mustard  Oil  (Hoffman's). 

The  primary  amins  treated  with  carbon  disulphide,  S  =  C  =  S 
(cf.  carbon  dioxide,  O  =  C  =  O)  afford  the  following  : 


64  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 


H2CNH2+CS2=CH8.  CH2NH-C-S-H 
CH3 

Ethylamin. 

The  C  of  the  CS2  joins  the  N,  and  the  displaced  H  joins  the 
S  which  has  been  deprived  of  one  valence. 

This  compound  is  now  treated  with  mercury  (Hg),  say  HgO, 
with  the  following  result : 

S 
C2H5-NH-CX 

s  ,HO 

C2H5— NH— C— S/ 

But  this  is  a  very  unstable  compound  and  at  once  breaks  up 
of  itself  into 


-  N  =  C  =  8)  +  HgS  +  H38. 

Ethyl  isothiocyanate  (a  mustard  oil). 

The  mustard  oils  are  the  isothiocyanates  (isothiocyanesters) 
of  alcohols  and  are  recognizable  by  their  pungent  odor. 

The  secondary  and  tertiary  amins  do  not  afford  the  above 
reactions  because  they  do  not  contain  enough  hydrogen  atoms 
to  enable  the  changes  to  take  place.  This  can  be  made  evident 
on  attempting  to  work  it  out  by  means  of  graphic  formulas  and 
equations. 

AMINO  ACIDS. 

To  the  physiological  chemist  the  amino  acids  are  the  most 
important  of  the  nitrogen  compounds  since  the  proteid  molecule 
is  almost  entirely  composed  of  them. 

Since  they  are  derived  from  the  alcoholic  OH  group  of  the 
oxyacids  we  may  recall  the  fact  that  such  an  OH  group  may  be 


NITROGEN  COMPOUNDS.  65 

attached  to  any  of  the  C  atoms  in  a  chain,  and  according  to  its 
position  as  regards  the  COOH  group  is  called  alpha,  beta, 
gamma,  etc. 

Just  so  with  the  amino  acids  : 


!H3 

2NH2 

a  amino  butyric  acid.  ft  amino  butyric  acid.  y  amino  butyric  acid. 

The  most  important  of  the  amino  acids  are  : 

COOH 

CHNH2 

<U2 


COOH 

CH2 

COOH 

CHNH2 

CH2 

CH2NH3 

CHS 

CHS 

Amino  ethanacid, 
aminoacetic  acid 
(glycocoll). 

Amino  propanacid, 
amino  propionic  acid 
(alanin). 

Aminohexanacid  , 
amino  caproic  acid 
(leucin). 

Leucin  may  occur  in  many  forms  : 

1.  As  alpha,  beta,  etc.,  according  to  the  position  of  the  NH2. 
The  leucin  of  the  proteid  molecule  is  always  in  the  alpha 

position. 

2.  Since  the  C  to  which  the  NH2  is  attached  is  asymmetric. 

COOH 
H— C— NH2 

CH3    etc. 

leucin  may  be  dextro-  or  Isevorotatory. 

The  leucin  of  the  proteid  molecule  is  nearly  always  Isevorota- 
tory. 
5 


66  OUTLINES   OF  PHYSIOLOGICAL   CHEMISTRY. 

3.  The  chain  may  be  normal,  iso  or  meso. 

)H  COOH  COOH 


NH2 


CH, 


INK, 


CH, 
CH8 


Normal.  Iso. 

The  leucin  of  the  proteid  molecule  is  nearly  always  iso,  and  is 
called  isobutylaminoacetic  acid.  But  it  is  perhaps  easier  to 
think  of  it  as  alpha  amino  caproic  acid. 

REACTIONS  OF  THE  AMINO  ACIDS. 

The  amino  acids  all  give  insoluble  azure  blue  salts  with 
copper,  and  in  this  way  can  be  isolated  as  a  group  in  crystal 
form. 

The  crystals  are  then  dissolved  in  hot  H2O  and  H2S  passed 
through  : 

NH3— CH2-CO 

p>Cu    -}-H2S=CuS-f  2(NH2-CH2 .  COOH) 

NH2-CH2  •  CO 

The  insoluble  CuS  falls  as  a  precipitate,  leaving  the  amino 
acid  in  solution. 

SEPARATION  OF  AMINO  ACIDS  FROM  EACH  OTHER. 
The  amino  acids  very  readily  form  ethylesters. 

CH3  •  CH2OH  CH 


+  =  >0    +H20 

NH2.CH2.COOH  NH2-CH2 

Ethy]  aminoace  tester . 


NITROGEN   COMPOUNDS.  67 

The  ethylesters  of  the  amino  acids  all  have  well-defined  boil- 
ing points  so  can  be  separated  by  fractional  distillation.  But 
being  very  unstable  the  distillation  must  be  carried  on  "in 
vacuo  "  at  low  temperatures  or  the  esters  will  break  up. 

Certain  characteristics  of  the  amids,  amins,  and  amino  acids 
may  be  considered  side  by  side  for  purposes  of  comparison. 

1.  Reaction. 

The  amids  are  neutral. 

A  base  NH3  combines  with  the  OH  of  an  acid  (cf.  mineral 
salts). 

The  amins  are  basic. 

There  is  no  acid  O  in  the  molecule  to  neutralize  the  base  NHa. 

The  amino  acids  are  both  acid  and  basic. 

Since  neither  the  acid  nor  the  base  are  in  direct  combination 
each  of  them  retains  its  own  characteristics.  The  amino  acids 
are  acid  by  virtue  of  their  COOH  group  and  at  the  same  time 
basic  by  virtue  of  their  NH2  group. 

2.  Action  of  Nitrous  Acid. 

Nitrous  acid  (HNO2)  acts  in  the  same  way  on  all  NH2 
groups  whether  amid,  amin,  or  amino.  It  has  the  power  of 
substituting  OH  for  the  NH2  group,  at  the  same  time  breaking 
up  the  latter  and  liberating  free  N. 

The  reaction  occurs  as  follows  : 


ff  !     I  ff 

K-C-iNjH3  =K-C-< 


-0-H+Na+H20 

+  HOiNlO 

Amid+niteous  acid,  Acid, 

K-CONHa+HN02.  R-COOH+Na+H20. 

K— CH, JNJH2  =    E— CH2OH+N2+H,O 

+  HO  JN  JO 

Amin.  Alcohol. 


68  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

COOH  COOH 

3         HC-    -  j  N  j  H,  =       HOOH  +N2  +H2O 

E+HOJNiO  K 

Amino  acid,  R—  CHNH2  •  COOH.  Oxyacid,  R—  CHOH-  COOH. 

HNO2  is  unstable,  passing  off  quickly  into  NO  and  NO2 
gases  (brown  fumes)  with  loss  of  H2O;  so  has  to  be  used  in  a 
nascent  condition. 

To  obtain  this  potassium  nitrite,  KNO2,  is  added  to  the 
solution  to  be  tested  and  then  H2SO4  : 

2KN02  +  H2S04  =  K2S04  +  2HNO2. 

The  liberated  HNO2  immediately  attacks  the  NH2  groups. 
It  is  its  desire  to  get  rid  of  its  OH  groups  which  is  the  cause 
of  this.  If  left  to  itself: 


o        +       0==0 

(NaO2  usually  called  NO.)  (Na04  usually  called  N02.) 

and  goes  off  in  brown  fumes,  but  it  is  able  to  get  rid  of  its 
OH  more  quickly  by  attacking  NH2  groups. 

If,  however,  HNO2  comes  in  contact  with  an  NH  (secondary 
or  imid  group)  the  action  is  different. 

>NiH  E—  Cv 

•R-<y    j  =  ^>N-N=0    +H20 

-fON|OH 

Secondary  NH  group.  Nitroso  combination. 

The  HNO2  parts  with  its  OH  which  combines  with  the 
single  H  to  form  H2O,  and  the  two  ISPs  combine  with  each 
other.  In  this  case  there  is  nothing  left  for  the  O,  so  it  remains 
attached  to  the  N  and  a  so-called  nitroso  compound  results. 
The  nitroso  =  N  —  N  =  O  reaction  is  often  of  value  for  the 
detection  of  NH  groups. 

HNO2  has  no  effect  on  a  triamin. 


NITROGEN  COMPOUNDS.  69 

E— C\ 

E-CAN 

K-C/ 

having  no  H  cannot  assist  HNO2  to  get  rid  of  its  OH,  so  the 
latter  goes  off  in  brown  fumes  in  the  ordinary  way,  leaving  the 
triamin  untouched. 

Sodium  hypobromite,  NaOBr,  in  alkaline  solution  will  also 
split  off  N  from  NH2  groups,  though  not  so  completely  as 
HNO2.  About  90  per  cent,  of  the  N  may  be  obtained  in  this 
way. 

The  reaction  with  urea  occurs  as  follows : 

1+iOiNaBr 
-j-NaBriO       /iN|H2i 

|O=C\ !  ^U  j  =C03+N2+2H80+3NaBr 

N:  1>  l-tlj; 

j  1+iOjNaBr 

This  test  is  simple  and  much  used  in  clinical  pathology  for 
estimation  of  the  amount  of  urea  in  urine.  But  it  is  not  accu- 
rate enough  for  quantitative  analysis  and  the  scientific  chemist 
leaves  it  severely  alone. 

The  test  is  made  in  a  fermentation  tube  and  the  amount  of 
gas  evolved  measured  as  N,  the  CO2  being  absorbed  by  the 
alkali  to  form  carbonates. 

OTHER  AMINO  ACIDS. 

Besides  the  monoamino-monobasic  acids  the  proteid  molecule 
contains  a  small  amount  of: 

1.  Monoamino-dibasic  Adds.  —  Of  these  the  most  important 

are : 

COOH 

!OOH  CHNH, 

!HNHa  CH, 

2  CH, 

COOH  COOH 

Amino  butandiacid,  asparaginic  acid.  Amino  pentandiacid  glutaminic  acid. 


70  OUTLINES   OF  PHYSIOLOGICAL   CHEMISTRY. 

These  contain  two  COOH  groups  to  one  NH2,  so  are  dis- 
tinctly acid.  Asparagin  is  sodium  asparaginate 

COONa .  CHNH2 .  CH2 .  COONa. 

2.  Diamino  Monobasic  Acids. 

!OOH 
HNH, 
H2 
H2 
H2 
._,-.-,  H2NH, 

Diamino  pentanacid  Diamino  hexanacid 

o,  8,  diamino  valerianic  acid  «,  e  diamino  caproic  acid 

(ornithin).  (lysin). 

These  contain  two  NH2  to  one  COOH,  so  are  distinctly  basic. 
It  will  be  observed  that,  like  leucin,  all  the  above  are  alpha 
amino  acids.  In  addition  ornithin  contains  NH2  in  the  delta, 
and  lysin  in  the  epsilon  position,  so  they  are  called  a,  8  amino 
valerianic  acid  and  a,  e  amino  caproic  acid  respectively. 

GLYCOSAMIN. 

Sugar  occurs  in  combination  in  the  proteid  molecule  as 
glycosamin. 

CHO .  CHNH2 .  CHOH .  CHOH .  CHOH .  CH2OH. 

Glycosamins  can  occur  as  insoluble  polymers  (cf.  glucose  and 
glycogen)  and  in  this  form,  called  chitosamin,  mixed  with  lime 
salts,  constitute  the  hard  chitinous  covering  of  lobsters  and 
other  crustaceae. 

Chitosamin  does  not  occur  in  vertebrate  animals.  Their 
bones  are  modified  proteids  (gelatin,  collagen)  mixed  with  lime 
salts. 

Cholin.  —  Before  leaving  the  subject  of  the  N  compounds  the 
constitution  of  cholin  may  be  given. 


NITROGEN   COMPOUNDS.  71 

Cholin  is  trimethyl  oxethyl  ammonium  hydroxide. 
Knowing  this  it  is  easy  to  construct  its  graphic  formula  : 
Ammonium  hydroxide  is 

j 

X-0-H 


Three  of  the  hydrogen  atoms  react  with  CH3OH,  making  : 
CH     CH, 

^>N—  OH  +  3H,O 
CH,   H 

The   remaining  H  reacts  with  ethandiol  (oxethyl  alcohol) 
(glycol). 
CHaOH  •  CHjOH+H-NsCCHj),      =      CHaOH  •  CH,—  N=(CH8)8+H,O 


Cholin. 

P  COMPOUNDS. 

Phosphorus  occurs  in  combination  in  the  proteid  molecule  in 
the  shape  of  lecithin. 

Lecithin  is  diolein  or  dipalmitin  or  distearin  cholin  phos- 
phoric acid  and  with  the  knowledge  already  gained  its  formula 
can  be  constructed. 

Taking  the  distearin  form  as  an  example  : 

H-CK 
H—  0-P= 


Phosphoric  acid. 


HC— O— St 
H2C— O— St 

J  Y 

Distearin  +  Phosphoric  acid.  Distearin  phosphoric  acicL 


72  OUTLINES   OF  PHYSIOLOGICAL   CHEMISTRY. 

H20 
HCOSt 
H2COSt    if' 

CH2  =  HCOSt     <>    CH2+H2O 

CH2OH          H2COSt     H    CH2OH 
Distearin  phosphoric  acid  +  Cholin  Lecithin. 

This  leaves  still  a  free  OH  group  on  the  phosphoric  acid  by 
which  it  can  attach  itself  to  some  other  component  of  the  pro- 
teid  molecule  with  loss  of  H2O. 

The  reason  for  calling  lecithin  a  phosphorized  fat  is  made 
clear  by  a  knowledge  of  its  constitution. 


CHAPTER  V. 

CYCLIC  COMPOUNDS. 

I.  THE  chains  of  C  atoms  have  a  tendency  to  curl  over  and 
join  at  the  two  ends,  forming  in  this  way  a  closed  chain.  In 
order  that  the  chains  may  close  up,  there  must  be  groups  at 
either  end  which  would  naturally  have  a  tendency  to  combine 
with  each  other. 

An  acid  COOH  group  would  have  a  tendency  to  combine 
with  an  alcohol  to  form  an  ether,  or  with  an  NH2  group  to 
form  an  imid,  NH. 

A  chain  therefore  with  COOH  at  one  end  and  NH2  at  the 
other  would  be  likely  to  close  up  if  the  chains  were  bent  over 
sufficiently  so  that  the  two  would  come  together. 

The  shorter  chains,  amino  acetic  acid,  amino  propionic  acid, 
are  not  able  to  bend  over  sufficiently  to  meet.  But  7  amino 
butyric  acid  is  long  enough,  and  the  same  may  be  said  of  all 
amino  acids  where  the  NH2  group  is  above  /3.  If  an  alcohol 
group  joins  with  a  COOH  group  the  compound  is  called  a 
Lactone,  and  COOH  combining  with  NH^  a  Lactam. 

H. 


0  +H,0 

H2C—  CH2  j..OH_J  H,C— 

y  oxybutyric  acid.  y  oxybutyric  lactone  (an  autoester). 

H2C—  CO 

H2c-cooH  y^ 

HaC-CH2NH,  H2C-CH, 

y  amino  butyric  acid.  -y  amino  butyric  lactam 

(an  auto  aminester). 

73 


74  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

II.  Again  two  or  more  separate  molecules  of  the  same  sub- 
stance may  condense  with  loss  of  H2O  or  NH3  and  form  a 
closed  chain.     Example,  cyanuric  acid  (page  60). 

III.  Two  or  more  similar  unsaturated  compounds  may  inter- 
change  a   valence   and   thus   form   a   closed   chain.     Ethine 
(acetylene  gas)   is  such   a  compound  HC  ==  CH.      If  three 
molecules  of  ethine  are  arranged  as  follows  ; 

CH 

%    (2) 

(Dl0  CH 

CH     CH 

*     (3) 
CH 

It  can  easily  be  seen  that  if  (1)  gives  up  a  valence  to  (2), 
(2)  to  (3)  and  (3)  to  (1)  the  resulting  molecule  will  appear  as, 


This,  by  far  the  most  important  of  the  cyclic  compounds,  is 
a  benzene  ring,  and  on  the  benzene  ring,  as  a  basis,  an  infinite 
variety  of  molecules  can  be  built  up. 

Benzene  may  combine  with  an  acid. 

In  the  case  of  an  alcohol  combining  with  an  acid  to  form  an 
ester  there  is  always  an  O  between  the  two  molecules. 


<?H8 


CYCLIC   COMPOUNDS.  75 

But  if  benzene  combines  with  sulphuric  acid  the  S  joins 
directly  on  to  the  C  without  any  intermediate  O,  and  the 
product  is  called  a  sulphonic  acid. 


Benzene,  CeH8.  Benzol  Bulphonio  acid,  CeH6  •  SO,H. 

In  the  same  way  benzene  treated  with  nitric  acid,  HNO3 

Cl 


Benzene,  CeH6.  Nitrobenzene,  C,H,  •  NO,. 

Nitrobenzene  is  the  basis  on  which  explosive  substances  are 
built  up. 

Ozybenzenes.  —  Any  of  the  H  atoms  attached  to  the  benzene 
ring  can  be  oxidized  to  OH,  but  obviously  no  further,  since 
there  is  only  one  valence  available  for  oxidation.  (Cf.  Tertiary 
alcohols,  p.  29.) 

If  one  H  is  oxidized  : 


CH 


Oxybenzene  (Carbolic 
acid)  (Phenol),  C6H6OH. 


It  makes  no  difference  which  of  the  H  atoms  is  oxidized,  the 
product  is  always  the  same. 

Supposing  the  OH  group  to  be  on  (2)  instead  of  (1) 


76  OUTLINES  OF  PHYSIOLOGICAL  CHEMISTRY. 

It  is  obvious  that  on  turning  the  page  on  which  this  is  printed 
one  sixth  of  the  way  round  (2)  will  be  where  (1)  was  before 
and  the  molecule  appears  as  in  the  first  example  given. 

Benzene  cannot  be  directly  oxidized  to  phenol  in  the  labora- 
tory, but  can  be  produced  artificially  in  a  round-about  way. 

For  convenience  the  CH  groups  and  the  double  links  are 
left  out  in  constructing  a  benzene  ring. 

MNO2 
+HN03  +H20 


Benzene,  CeH6.  Nitrobenzene,  C6H5-  N02. 

On  treating  nitrobenzene  with  nascent  H  the  NO2  is  reduced 

toNH2 

N02  /\  NH2 

+3H2  [       |  +2H20 

\/ 

Nitrobenzene,  C6H6-  N0a.          Phenylamin  (Anilin),  C6H6.  NH2. 

Nascent  H  may  be  produced  by  stannous  chloride  and  an 

alkali 

Sn— Cl 

|  +2NaOH    =    2SnO    +    2NaCl    +    H2 

Sn— Cl 

(For  other  methods  of  obtaining  H  see  p.  14.) 
The  NH2  group  of  phenylamin  is  affected  by  HNO2  in  pre- 
cisely the  same  way  as  NH2  groups  of  the  open  chain  amins 
already  discussed. 

0—  !NIH2  /\OH 

+  !  =       (    )      +N2+H20 

HOiNjO  \/ 

Phenylamin  +  nitrous  acid  Phenol. 

C6HB-  NHa  +  HN02  C6H6-  OH. 

The  final  product  being  artificial  phenol. 

But  if  this  last  process  is  conducted  at  a  very  low  tempera- 
ture, below  freezing  point,  the  reaction  is  different ;  somewhat 
analogous  to  the  nitroso  reaction. 


CYCLIC   COMPOUNDS.  77 

In  this  case  the  N  does  not  leave  the  benzene  ring  but  joins 
itself  to  the  N  of  the  HNO,  with  two  valences. 


'\ NilL 

+  =        I      I  4-HjO 

HONjO  \/ 

Anilin  +  nitrous  acid  Diazobenzene, 

C6H6-  NOa  +  HNOa  C.H.-  NaOH. 

Diazobenzene  is  the  basis  for  anilin  dyes  and  if  our  object 
were  to  study  the  anilin  dyes  we  could  follow  up  the  subject 
in  this  direction.  But  the  anilin  dyes  do  not  concern  us  here. 

The  process  of  obtaining  phenol  may  be  summarized : 

1.  C6H6  Benzene 

2.  C6H5.NO2      Nitrobenzene 

3.  C6H5.NH2     Anilin 

4.  C6H5.OH      Phenol 

The  alcohol  OH  group  of  an  open  chain  is  basic  (p.  36). 
The  alcohol  group  of  a  benzene  ring  is  slightly  acid.     In 
consequence  of  this,  their  reactions  are  somewhat  different. 
Phenol  for  example  will  not  form  esters  with  an  acid. 

MILLON'S  KEACTION. 

If  phenol  is  heated  with  Millon's  reagent  (which  is  a  mixture 
of  mercuric  and  mercurous  nitrate  containing  some  free  nitrous 
acid)  a  red  color  is  produced. 

The  color  is  the  result  of  a  reaction  between  the  reagent  and 
a  single  free  OH  group  attached  to  a  benzene  ring.  No  matter 
what  else  is  attached  to  the  ring,  so  long  as  there  is  a  single 
free  OH  group  the  substance  will  afford  the  reaction. 

Most  proteid  material  gives  Millon's  reaction,  indicating  that 
in  its  composition  there  is  a  benzene  ring  with  one  free  OH  group 
attached. 

It  has  been  said  that  nitrobenzene  is  the  basis  of  explosives. 
Since  the  study  of  explosives  is  not  our  object  this  branch  will 


78  OUTLINES   OF  PHYSIOLOGICAL  CHEMISTRY. 

not  be  followed  up,  but  one  nitro  compound  may  be  mentioned, 

OH 


'2 

Trinitro  oxybenzene  (Picric  flcid), 

The  presence  of  so  much  O  makes  the  OH  group  a  strong 
acid  in  this  case  so  that  picric  acid  will  combine  with  bases 
much  more  readily  than  phenol. 

Picric  acid  has  a  bright  yellow  color  and  this  is  a  character- 
istic of  all  nitrobenzenes. 

XANTHOPKOTEIC  REACTION. 

Proteids  give  a  yellow  color  on  warming  with  nitric  acid. 

This  indicates  the  presence  of  a  benzene  ring ;  a  nitrobenzene 
being  formed. 

In  this  case  it  is  not  necessary,  as  with  Millon's  reaction,  for 
the  benzene  ring  to  have  an  OH  group  attached. 

DIOXYBENZENES. 

A  second  OH  group  of  a  benzene  ring  may  be  oxidized  and 
in  this  case  we  have  a  dioxybenzene. 

According  to  the  position  of  the  OH  groups  as  regards  each 
other  there  are  three  possible  different  combinations  among  the 
dioxybenzenes. 

Each  combination  forms  a  distinct  compound  which  differs 
in  some  of  its  reactions  from  the  other  two. 

The  three  different  dioxybenzenes  are  : 

a[  OH 

n 
\/OH 

Orthodioxybenzene  Meta  dioxybenzene  Paradioxy  benzene 

(Catechin),  (Resorcin),  (Hydrokinone), 

C6HV  (OH),  C6H4.  (OH)a  C6H4.  (OHa) 


CYCLIC   COMPOUNDS.  79 

The  empiric  formula  of  each  is  the  same,  but  the  arrange- 
ment of  the  OH  groups  on  the  ring  is  different.  If  the  two  OH 
groups  lie  next  to  each  other  the  compound  is  designated  as 
"  ortho."  If  one  CH  group  lies  between  the  two  OH  groups 
as  it  is  called  "  meta."  If  two  CH  groups  lie  between  the  two 
OH  groups  it  is  called  "  para." 

The  dioxybenzenes  are  reducers,  i.  e.,  they  have  the  power  of 
abstracting  O  from  certain  other  compounds  with  the  formation 
of  quinones. 

In  the  presence  of  alkalis  they  can  take  up  O  from  the  air 
and  form  quinone. 

The  metadioxybenzene  has  little  power  of  doing  this.  It  is 
a  feeble  reducer. 

The  ortho-dioxybenzene  is  stronger,  but  the  para  is  the  most 
active  reducer  of  the  three 


/\ 


QH  /\\ 

i       i       i  t-\     (free  in  air  or  in     I  V          ,  TT  n    or  i*  maJ  be 

'I  combination)    :  =1   1   I  put  as 

OH  \l/ 

Paradioxybenzene  =  Quinone, 

hvdrokinone,  CtH4O2. 

C8H4.  (OH),. 

REACTIONS. 

All  the  dioxybenzenes  give  an  emerald  green  color  with 
FeCl3.  Adrenalin  gives  an  emerald  green  color  with  FeCl3 
and  this  is  due  to  the  presence  in  it  of  catechin  in  combination. 

Catechin  alone  does  not  raise  the  blood  pressure,  but 
in  combination  with  some  other  substance  the  exact  con- 
stitution of  which  is  not  certain,  forms  the  active  principle 
of  adrenalin. 

The  dioxybenzenes  do  not  give  Millon's  reaction.  This  only 
occurs  with  substances  which  have  a  single  OH  group  on  the 
ring. 


OF   ^ 


80  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

JResorcin  is  used  as  a  test  for  ketoses.  Its  crystals  are  added 
to  a  solution  containing  a  ketose  and  warmed.  A  red  color  and 
later  brown  precipitate  soluble  in  alcohol  is  formed. 

TRIOXYBENZENES. 

Three  of  the  CH  groups  of  benzene  may  be  oxidized  and, 
as  with  the  dioxybenzenes,  different  compounds  are  formed 
according  to  the  positions  of  the  OH  groups. 

OH  OH  OH 

fl  °H  II  °H  II 

tJ  OH  LJ  OH  I'  OH 

OH 

Ortho  trioxybenzene.  Meta  Para  trioxybenzene. 

Pyrogallol.  trioxybenzene.  Phloroglucin. 

The  trioxy  benzenes  are  also  reducers  with  formation  of  quin- 
ones,  the  ortho  form  being  here  the  most  active.  Pyrogallol 
therefore  is  used  as  a  developer  in  photography,  a  case  where 
an  active  reducer  is  needed. 

Pyrogallol  reduces  even  more  actively  than  hydrokinone,  and 
is  much  used  in  making  determinations  of  oxygen,  by  measuring 
the  diminution  in  volume  of  a  gas,  caused  by  shaking  it  in  an 
alkaline  solution  of  pyrogallol. 

Both  hydrokinone  and  pyrogallol  will  reduce  Fehling's 
solution. 

)H 


+CuO  =  +Cu20+H20 

/p 


H 
+CuO  I     +Cu20+H2O 


It  is  evident,  therefore,  that  in  their  reducing  power  these 
di  and  trioxybenzenes  possess  the  characteristics  of  aldehydes. 


CYCLIC   COMPOUNDS.  81 

Phlorogludn  with  HC1,  added  to  a  solution  of  pentose  and 
warmed,  affords  a  red  color.  This  is  used  as  a  test  for  pentoses. 

SUBSTITUTION  PRODUCTS  OF  BENZENE.      % 

The  H  of  the  benzene  ring  can  be  replaced  (substituted)  by 
various  compounds,  for  instance,  methane,  ethane,  etc.,  and 
these  can  be  oxidized  in  the  usual  way. 

C/\C-CHS  /\CH,OH  /\CHO  /\  COOH 

C\/C  \/  \7  \S 

Methan  benzene  Methanol  benzene  Methanal  benzene  Methan  acid 

(Toluol),  C6HB  •  CH3.         (Benzoyl  alcohol),          (Benzoyl  aldehyde),       benzene  (Ben- 
C6HB  .  CHaOH.  C6H6  •  CHO.  zoic  acid), 

C6H6  .  COOH, 

The  substitution  products  of  benzene  are  infinite  in  number 
and  for  further  particulars  the  reader  must  be  referred  to  the 
text-books. 

EXCRETION  OF  BENZENE  KINGS. 

The  cyclic  compounds  are  very  stable  bodies  and  cannot  be 
broken  up  by  oxidation  in  the  body.  A  benzene  ring  absorbed 
through  the  intestine  is  excreted  as  such  in  combination  with 
something  else. 

1.  A  phenol  (OH)  is  excreted  as  an  acid  ester. 

(a)  In  combination  with  sulphuric  acid  as  a  phenol  sulphuric 
acid. 

.      ft  /\          ff 

— ;  6— H  H !  O— S— O—  H     =       f       |  — O— S— O— H 

O  I  +H.O 

Phenol +sulphuric  acid.  Phenol  sulphuric  acid. 

It  has  been  said  that  the  OH  group  of  an  oxybenzene  is 
slightly  acid  and  has  no  affinity  for  acids.     This  is  true  in  a 
general  way,  but  the  reaction  does  occur  in  the  body. 
6 


82  OUTLINES  OF   PHYSIOLOGICAL   CHEMISTRY. 

Phenolsulphuric  acid  itself,  however,  is  very  unstable,  and 
the  product  excreted  is  in  the  shape  of  phenol  potassium  sul- 
phate which  is  more  stable. 


Phenol  potassium  sulphate. 

(6)  In  combination  with  glycuronic  acid  as  phenol  glycuronic 
acid. 

II.  If  an  acid  COOH  group  is  attached  to  the  benzene  ring 
it  is  excreted  as  glycocoll  aminester.  If  benzoic  acid,  for  in- 
stance, is  fed  to  an  animal,  hippuric  acid  is  excreted  in  the 
urine. 

O  O 

(^  —  C— 16— H+HIHN  •  CH3 .  COOH=  i       |  — C— NH  -  CH2  •  COOH 

k/  \/  +H3° 

\/  \/ 

Benzoic  acid,  -f-  glycocoll,  =  Benzoyl  glycocoll  aminester, 

C6H6-  COOH  CHaNH2-  COOH  (Hippuric  acid), 

C6HS-  CO-  NH-  CHa-  COOH. 

Briefly  summarizing : 

1.  An  OH  benzene  ring  is  excreted  as  an  acid  ester  (sul- 
phuric, glycuronic). 

2.  A  COOH  benzene  ring  is  excreted  as  an  aminester  (gly- 
cocoll). 

The  glycocoll  aminesters  leaving  the  body  in  this  way  are 

all  called uric  acid,  although  they  have  in  reality 

nothing  in  common  with  uric  acid  itself. 

Salicylic  acid  is  ortho-oxybenzoic  acid. 

OH  OH  ft 

,/N  COOH  f\  C  •  NH  •  CH,  •  COOH 

I    J  and  it  leaves  the  body  as      I     J 

Salicylic  acid.  Salicyluric  acid, 

C0H4(OH)*.  (COOH)».  C6H4-  (OH)i-  (CO-  NH-  CH2-  COOH)2. 

(The  small  numerals  indicate  the  position  on  the  ring.) 


CYCLIC   COMPOUNDS.  83 

In  this  case  the  stronger  COOH  reaction  takes  place  instead 
of  the  weaker  OH  one ;  an  aminester,  not  an  acid  ester,  being 
formed. 

Oxybenzoic  acid  can  occur  in  three  forms : 

)H 


Ortho. 

CRESOLS. 

The  cresols  will  be  referred  to  later  on  and  their  construction 
may  be  given  here.     They  are  methyloxybenzenes. 

OH  OH 

OCH, 


Ortho.  Meta. 


Tricresol,  much  used  as  an  antiseptic,  is  a  mixture  of  these 
three.  Lysol  is  a  mixture  of  paracresol  and  soap. 

The  cyclic  compounds  occurring  in  plants  are  of  great 
variety  and  those  which  can  be  synthesized  in  the  laboratory 
almost  infinite  in  number. 

A  large  number  of  them  emit  powerful  odors,  agreeable  or 
the  reverse,  and  the  group  is  consequently  often  called  aro- 
matic. Aromatic  or  cyclic  compounds.  Proteids,  however, 
are  very  poor  in  cyclic  compounds.  Of  the  isocyclic  only  two, 
tyrosin  and  phenylalanin,  so  far  as  is  known,  occur  in  combi- 
nation in  the  proteid  molecule. 


2  •  CHNH2  •  COOH  CH2  •  CHNH2  •  COOH 

Paraoxyphenylamino  propionic  acid  Phenylamino  propionic  acid 

(Tyrosin).  (Phenylalanin). 


84  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

Tyrosin  obviously  will  give  Millon's  reaction,  whereas 
phenylalanin  does  not.  These  compounds  will  be  referred  to 
again. 

Now  that  the  constitution  of  the  benzene  ring  is  known, 
certain  reactions,  which  some  of  its  derivatives  give  with  sub- 
stances already  discussed,  may  be  mentioned. 

The  principal  benzene  derivatives  used  for  these  reactions 
are : 

1.  Benzoyl  chloride. 

2.  Phenyl  isocyanate. 

3.  Phenyl  hydrazin. 

1.  Benzoyl  chloride  is  benzoic  acid  in  which  OH  is  replaced 
byCl. 

)-H|  /\  C-C1 

hTT '  Ol  \.          s  ~T~-"-2^-' 

XI  !  \JL  \^      / 

Benzoic  acid + Hydrochloric  acid,  Benzoyl  chloride,  C6H5  •  COC1 

C6H6  •  COOH 

2.  Phenyl  isocyanate  is  isocyanic  acid  in  combination  with 
phenol. 

^\  _N=C=0 

H  LN=C=O  =  \/  +H2° 

Phenol  -f  isocyanic  acid,  Phenyl  isocvanate, 

C6-  H6-  OH  +  HNCO  C6H6-  NCO 

3.  Phenylhydrazin. 

To  understand  the  constitution  of  phenylhydrazin  NH3 
must  first  be  referred  to. 

As  a  rule  when  an  OH  group  is  attached  to  N  the  latter  is 
pentatomic  thus  : 

TT  TT 

r— H  +  H2o  =     /N^O 

H       XH 


CYCLIC   COMPOUNDS.  85 

But  one  of  the  H  atoms  attached  to  NH3  may  exceptionally 
be  oxidized  without  N  becoming  pentatomic. 

H  H 

Jf— N— H    +    O    :       H-N-O— H 

Ammonia.  Hydroxylamin. 

The  reason  for  calling  this  an  amin  is  obvious,  for  if  the  C3 
is  replaced  by  —  C  ==  R  we  have  one  of  the  ordinary  amkis 
with  which  we  are  already  familiar. 

Hydroxylamin  may  unite  with  NH3  with  loss  of  water  : 


7 .          -7 

_^_i  6-S'TH  1-i-H  = 


H2N-NH2    +    H20 

Hydroxyl  amin    +    Ammonia    =    Hydrazin,  N2H4. 

When  an  N  is  attached  to  another  N  this  is  designated  by 
—  az  —  .     Thus  we  have  : 

=  N-N=  -N  =  N- 

Azo  compound.  Diazo  compound. 

Hydrazin  does  not  occur  free  but  only  in  combination,  mainly 
with  organic  compounds  —  open  or  closed  chains  : 


0 


— ;O  -H+H;HN  •  NH2        =         /  \  — NH  •  NH2 

kj  +H20 

Phenol +hydrazin.  Phenyl  nydrazin. 


REACTIONS  WITH  BENZOYL  CHLORIDE  AND 

PHENYLISOCYANATE. 
It  is  much  easier  to  isolate  a  substance,  i.  e.,  to  get  it  in 
pure  form  free  from  impurities,  if  it  is  crystallizable  rather 
than   amorphous.     Crystals  are  definite  bodies  with  definite 
melting  points,  which  is  seldom  the  case  with  amorphous  forms. 
Substances  belonging  to  the  open  chain  series,  as  a  rule,  do 
not  crystallize  well,  whilst  the  cyclic  compounds  readily  do  so. 


86  OUTLINES   OF   PHYSIOLOGICAL    CHEMISTEY. 

If  one  pictures  to  oneself  a  number  of  single  chains  lying 
about,  it  is  difficult  to  imagine  that  on  drying  out  they  would 
arrange  themselves  in  any  particular  order  or  shape.  On  the 
contrary  a  number  of  benzene  rings  might  easily  be  supposed 
to  fit  into  each  other  and  build  up  a  crystal. 

Diagrammatically : 


The  object  then  is  to  find  some  way  of  getting  a  substance 
which  crystallizes  badly  to  crystallize  well,  or  to  get  a  volatile 
body  to  crystallize. 

By  attaching  it  to  a  benzene  ring  a  crystallizable  substance 
is  produced.  This  product  can  be  isolated,  the  benzene  ring 
driven  oif,  and  the  original  substance  thus  obtained  in  pure 
form,  the  benzene  ring  merely  serving  as  a  medium. 

Benzoyl  chloride  and  phenylisocyanate  are  used  as  media, 
and  the  process  is  called  benzoylizing,  an  expression  constantly 
met  with  in  reading  articles  on  physiological  chemistry. 

The  Cl  of  benzoyl  chloride  is  only  loosely  attached  and  is 
readily  given  up  to  an  alcohol  OH  group  to  form  an  ester,  or 
to  an  NH2  group  to  form  an  aminester. 

The  reaction  occurs  in  alkaline  solution  as  follows  : 


/V-C-!  ci  I  /\  -CO  •  O  -  CH2 .  CH3 

I      I  = 


-fjHj— O— CH2-CHS 


+HC1 


Benzoyl  chloride  +  ethanol,  =  Ethyl  benzoyl  ester, 

C6HB-  COC1.  C6HV  COO-  CHa-  CH3 

The  alcohol  has  been  benzoylized. 


CYCLIC  COMPOUNDS.  87 

The  above  is  merely  given  as  a  simple  example  of  the  reac- 
tion which  occurs  with  an  alcohol.  As  a  matter  of  fact  ethyl- 
benzoyl  ester  does  not  crystallize,  but  is  an  oily  fluid  which, 
however,  is  easily  separated  out.  But  the  polyatomic  alcohols, 
and  more  particularly  the  monosaccharides,  afford  easily  crystal- 
lizable  products  with  benzoyl  chloride. 

(2)  With  amids,  amins,  and  amino  acids,  benzoyl  chloride 
in  alkaline  solution  forms  aminesters. 


-C-jCl  i  /\  -C- 


0-C-[C1 1  />  -C-NH  •  CH2  -  COOH 

+JHJHN-CH2-COOH   =    \/  +HC1 

Benzoyl  chloride  +  glycocoll.  =  Benzoyl  glycocoll  aminester. 

The  glycocoll  has  been  benzoylized. 

In  benzoyl  glycocoll  aminester,  hippuric  acid  will  be  recog- 
nized again.  It  can  therefore  be  produced  in  the  laboratory 
as  well  as  in  the  body. 

Phenylisocyanate  is  used  for  the  same  purpose  as  benzoyl 
chloride.  It  affords  more  definite  compounds  than  benzoyl 
chloride,  so  is  more  valuable  for  accurate  work,  but  its  expense 
prevents  its  use  in  the  laboratory  for  ordinary  purposes. 

The  reaction  with  NH2  groups  may  be  given,  taking  glycocoll 
again  as  an  example. 

-N=C=O  /\  _ NH— C— NH  •  CH2  •  COOH 

+NH2.CH2-COOH  =     yj 
Phenyl  isocyanate  +  glycocoll.  Phenyl  glycocoll  isocyanate. 

It  will  be  observed  that  in  this  case  there  is  no  loss  of  water. 
The  C  of  the  N  =  C  =  O  group  detaches  one  valence  from  the 
N  to  join  to  the  NH2  group,  and  the  H  thus  liberated  attaches 

itself  to  the  first  N  and  saturates  it  again. 

_  _  o 

]  %^  I  =     E-NH-C-NH-R 

H      -NH-E 


88  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

A  curious  point  about  the  aminisocyanates  may  be  brought 
out  by  substituting  H  for  the  radical  on  either  side  of  the 
isocyan  group. 

R— iNH— 0— NH|-E        makes        H2N— C-NHa 
JH  HJ 

or  urea,  so  that  we  may  regard  the  isocyanates  as  merely  sub- 
stituted urea. 

PHENYL  HYDRAZIN,  H6C5.  NH.  NH2. 

The  NH2  very  readily  gives  up  its  two  free  H  atoms  to  an 
aldehyde  or  ketone  group,  the  H  atoms  attaching  themselves 
to  the  aldehyde  or  ketone  O  to  form  H2O  and  the*N  to  the  C 
by  two  valences 

j/^j-NH-NiH.+okCH  i/^-NH— N=CH 

'  k  =  I   I          ™  +H°° 


Phenyl  hydrazin' -f  ethanal,  =        |        Phenyl  ethyl  hydrazone, 

C6HB-  NH-  NH2.  C6H6-  NH-  N-  CaH4. 

This  reaction  is  much  used  as  a  test  for  aldehydes  and  ketones, 
the  resulting  hydrazones,  as  they  are  called,  crystallizing  easily. 
^^^  The  osazone  test  for  sugars  is  based  on  this  reaction  but  here 
the  process  is  more  complicated. 

If  to  a  solution  of  a  hexaldose  (glucose)  phenylhydrazin  is 
added  and  the  mixture  warmed,  three  successive  reactions  occur. 


"KTTT      TVT'TT     t   /\> /">TT       />/"^TIT/"\TT\       /"ITT  /~\TT 

, — IsJti — IS:ri2-(-(J.=:Cil2  •  (CHOHj^  •  Cli2OH 
- ! 

=     /^j  — NH— N=CH  •  ( CHOH)<  •  CH2OH  +H2O 
\/ 

Phen  yl  hydrazin  +  Glucose  =  Phenyl  glucose  hydrazone. 

(2)  A  second  molecule  of  hydrazin  now  attacks  the  group 
lying  next  to  the  aldehyde  group,  depriving  it  of  its  two  hydro- 


CYCLIC   COMPOUNDS.  89 

gen  atoms  ;  at  the  same  time  forming  anilin  with  release  of 
NH3.     The  CHOH  group  of  the  sugar  thus  attacked  has  only 
an  O  left  and  becomes  a  ketone. 
HC=N-NH  •  C6H5  /\  HC=N  -  NH 


OH)8  (CHOH), 

2OH  CH3OH 

Phenyl  hydrazin  +  Phenylglucosehydrazone  Intermediate  body. 

(3)  The  ketone  thus  formed  is  immediately  attacked  by  a 
third  phenylhydrazin  molecule  as  follows  : 

HC=N  -  NH  •  C6H6  HC=N  •  NH 


(CHOH)3 

:2OH 

Intermediate  body  +  Phenyl  glucose  hydrazone  =  Glucosazone  (an  osazone). 

"With  ketoses  the  ketone  C  =  O  group  is  always  next  to  one 
of  the  end  CH2OH  groups,  so  that  the  ketone  group  of  a 
ketose  may  be  regarded  as  holding  an  alpha  position. 

Phenylhydrazin  brought  in  contact  with  a  hexketose  (fruc- 
tose) first  forms  a  phenylketosehydrazone  with  the  ketone 
group. 

A  second  molecule  of  the  phenylhydrazin  then  deprives  the 
adjacent  CH2OH  group  of  its  hydrogen  atoms,  forming  anilin 
and  NH3. 

This  newly  formed  aldehyde  group  then  reacts  with  a  third 
molecule  to  form  the  osazone.  Thus,  although  in  this  case  we 
start  with  a  ketose  (fructose),  the  final  product  is  precisely  the 
same  as  with  an  aldose  (e.  g.,  glucose). 

This  can  be  easily  verified  on  working  out  the  reaction,  with 
the  help  of  graphic  formulas.  In  each  case  a  definite  crystal- 
lizable  substance  with  a  definite  melting-point  is  obtained,  but 


90  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

the  two  substances  may  be  precisely  alike,  providing  their  re- 
maining H  and  OH  groups  are  arranged  in  the  same  way. 
Where  these  differ  the  osazones  will  differ  slightly  in  solubility, 
so  that  to  a  limited  extent  monosaccharides  may  be  differenti- 
ated by  means  of  their  osazones. 

DOUBLE  KINGS. 

To  the  benzene  ring  a  second  ring  may  be  attached  to  form 
naphthalene,  and  this  may  be  oxidized  to  naphthol. 


\/OH 
OH 

Naphthalene,  a  naphthol,  /3  naphthol, 

CJOH8  C10H7OH  C10H7OH 

On  the  double  ring  it  makes  a  difference  whether  the  OH 
group  lies  next  to  the  link,  as  the  alphas,  or  one  removed  from 
it  as  the  betas.  It  makes  no  difference  on  which  of  the  four 
alphas  the  OH  is  placed.  Its  relations  to  the  rest  of  the  mole- 
cule are  the  same  in  each  instance,  and  the  same  is  true  of  the 
four  beta  positions.  There  are  therefore  two  naphthols,  a 
and  ft. 

MOLISCH'S  REACTION  FOR  SUGARS. 

If  an  alcoholic  solution  of  a  naphthol  is  added  to  a  solution 
containing  sugar,  or  any  carbohydrate,  and  a  little  H2SO4  then 
carefully  poured  down  the  side  of  the  tube,  the  latter  sinks  to 
the  bottom  and  at  the  point  of  junction  a  violet  color  at  once 
appears,  due  to  formation  of  furfurol. 

This  is  a  very  delicate  reaction,  occurring  even  if  the  sugar 
is  in  combination.  Proteid  material  containing  glycosamin  in 
combination  gives  it. 

CHOLESTERIN 

is  a  fat-like  substance,  which  however  is  not  a  true  fat,  but  a 
higher  monoatomic    alcohol,  the  empirical  formula  of  which 


CYCLIC    COMPOUNDS.  91 

is  C^H^OH.  Since  there  are  not  enough  hydrogen  atoms  to 
form  a  chain  it  is  supposed  there  must  be  a  benzene  ring  in  it 
somewhere,  but  its  constitution  is  not  understood. 

GLUCOSIDES 

are  glucose  combined  with  some  cyclic  alcohol  to  form  glucose 
ethers.  Glucosides  do  not  reduce  Fehling's  solution  or  form 
osazones,  so  it  is  probable  that  the  aldehyde  group  enters  into 
the  combination.  (Cf.  Disaccharides,  p.  50.) 

Example : 

OH  OH 

\  CH2OH  f\  CH2   —  glucose 

LJ  +  glucose  =         I       I  +H20 

Salicyl  alcohol  =  Salicin. 

Salicin  is  found  in  the  bark  of  the  willow. 

There  are  a  large  number  of  glucosides,  but  since  they  are 
exclusively  products  of  plant  life,  never  being  found  in  animal 
tissues,  they  need  not  detain  us. 


HETEROCYCLIC  COMPOUNDS. 

If  the  ring  or  one  of  the  rings  contains  fewer  than  six  carbon 
atoms  it  is  irregular  and  is  called  heterocyclic. 
One  of  the  six  C  atoms  may  be  replaced  by  N 

C/\C  C/\C 

C\^C  C\Al 

c  IT 

Benzene.  Pyridin. 

Or  the  ring  may  consist  of  four  C  atoms  with  NH,  S,  or  O. 
Thus: 

C  C, ;C 


C 
IB.  s  06 

Pyrrol.  Thiophen.  Furan.  Furfurol. 


92  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

As  is  the  case  with  the  isocyclic,  the  proteid  molecule  is 
poor  in  heterocyclic  compounds.  There  is  in  fact  only  one  of 
importance,  a  ring  of  which  indol  is  the  best  known  repre- 
sentative. Indol  has  a  double  ring,  of  which  one  is  irregular. 


COH 


Indoxylsulphuric  acid  (urine  indican). 

Indol  is  oxidized  to  indoxyl  in  the  body  and  in  consequence 
of  the  OH  group  is  excreted,  like  phenol,  in  combination  with 
sulphuric  acid  (urine  indican). 

Urine  indican  must  not  be  confounded  with  the  indican 
of  the  indigo  plant  which  is  a  glucoside  (glucose  +  indoxyl, 
p.  91). 

Indol  is  formed  in  the  large  intestine,  by  the  action  of 
bacteria,  principally  coli  communis,  as  a  product  of  the  decom- 
position of  the  proteid  molecule. 

Normally  the  indol,  or  by  far  the  greater  part  of  it,  passes 
off  with  the  feces,  but  if  there  is  intestinal  obstruction,  or  an 
unusual  amount  of  intestinal  putrefaction,  the  indol  may  be 
largely  absorbed  in  the  body  and  undergoes  the  changes  m^^ 
tioned  above. 

Indoxyl  is  easily  oxidized  to  indigo 

^    11       !C°  C°l        I!       :i     +     2H20 


/\ 

'\/CH 
NH 

Indoxyl. 


Indigo  blue. 


CYCLIC   COMPOUNDS.  93 

As  soon  as  oxidation  occurs  one  link  between  the  CO  and 
CH  is  released.  Two  molecules  then  combine  as  above,  each 
losing  H2  which  combines  with  O  to  form  H2O. 

Along  with  the  indigo  blue  a  small  amount  of  indigo  red  is 
also  formed.  Indigo  red  is  the  same  as  indigo  blue  but  with 
one  of  the  indol  rings  reversed.  The  two  are  space  isomers. 


H  NH  NH     CO 

Indigo  blue.  Indigo  red. 

Indicanuria  or  indican  in  the  urine  can  be  experimentally 
produced  in  animals  by  resecting  a  portion  of  the  intestine  and 
replacing  it  inversely.  In  this  portion  peristalsis  is  reversed, 
and  there  is  obstruction.  Coli  communis  and  other  bacteria 
are  able  to  multiply  at  any  such  point,  even  if  it  is  in  the  upper 
part  of  the  small  intestine  where  they  do  not  normally  exist. 

Indol,  therefore,  is  formed  in  excess  and  appears  in  the  urine 
as  iudican. 

Besides  indol,  skatol  or  methyl  indol  is  formed  by  bacteria  in 
the  intestinal  tract,  and  it  is  to  this  that  the  fecal  odor  is 
mainly  due. 


/  \:OOH 

TH  NH  NH 

Indol.  Skatol.  Skatol  carbonic  acid. 


Skatol  carbonic  acid  is  also  a  product  of  proteid  decomposition 
by  bacteria. 

xs. 

CH, 

XCHNH2-  COOH 


H 

Tryptophan. 


Tryptophan  or  skatol  amino  acetic  acid,  exists  in  combina- 
tion in  the  proteid  molecule.     (See  postscript.) 


94  OUTLINES  OF  PHYSIOLOGICAL  CHEMISTRY. 

REACTIONS. 

Indol  treated  with  H2SO4  and  KNO2  gives  a  red  color,  due 
to  the  production  of  nitroso  indol. 

H2S04  +  2KN02  =  K2S04  +  2HNO2 

nascent  nitrous  acid. 


+H20 

H  N— N=0 

+  ON  |  OH 
Indol  +  nitrous  acid  Nitroso  indol. 

Nitroso  skatol  and  the  nitroso  .compounds  of  the  other 
derivative  of  indol  do  not  afford  the  red  color. 

Tryptophan  if  free  gives  a  pinkish  color  with  chlorine  or 
bromine  water. 

Tryptophan  in  combination  in  the  proteid  molecule  does  not 
afford  this  reaction,  but  it  will  give  a  violet  color  if  treated 
with  H2SO4  and  acetic  aid  (Adamkievicz  reaction). 

It  has  long  been  known  that  if  the  acetic  acid  has  been 
freshly  made  it  will  not  give  the  Adamkievicz  reaction.  But 
it  has  only  recently  been  shown  that  it  is  not  the  acetic  acid 
itself  which  reacts,  but  an  oxidation  product,  glyoxylic  acid. 

CH3  COOH  +  O2     =     CHO.  COOH  +  H2O 

Acetic  acid.  Ethanal  acid  (Glyoxylic  acid). 

Sodium  glyoxylate  can  be  easily  made  by  reduction  of  oxalic 
acid  with  sodium  amalgam  and,  since  this  is  stable,  it  is  now 
used  instead  of  old  acetic  acid  for  the  test.  (Hopkins  reaction.) 

Na.Hg      +  COOH.COOH  =  CHO.COONa  -f  HfO  +  Hg. 

Sodium  amalgam.  Oxalic  acid.  Glyoxylic  acid. 

The  Hg  merely  serves  as  a  restrainer  for  the  Na,  which 
would  react  too  violently  if  used  alone. 

On  adding  H2SO4  the  Na  is  driven  off  and  the  glyoxylic  acid 
gives  the  violet  color  with  the  tryptophan. 


CYCLIC   COMPOUNDS.  95 

The  structure  of  the  colored  product  is  not  known. 

The  alkaloids  are  complicated  vegetable  products,  the  con- 
stitution of  only  a  few  being  known.  There  are  three  rings 
which  chiefly  serve  as  a  basis  for  their  make  up. 


N 
\/  \/ 

N  N 

Pyridin.  Chinolin.  Isochinolin. 

The  alkaloids  are  largely  poisonous  but  do  not  directly  con- 
cern us  except  for  the  fact  that  at  one  time  they  were  supposed 
to  be  products  of  plants  solely. 

If,  therefore,  alkaloids  were  found  in  a  body  "  post-mortem," 
it  was  taken  for  granted  that  death  was  caused  by  vegetable 
poisoning  and  many  a  man  has  been  hanged  on  this  evidence. 

It  is  now  known,  however,  that  this  is  an  erroneous  supposi- 
tion, for  many  bacteria  produce  alkaloids  and  after  decomposition 
has  set  in  alkaloids  may  be  found  in  animal  organs  without  death 
having  been  necessarily  caused  by  them. 


PUKIN 

Although  the  purin  bases  are  cyclic  compounds  they  can 
hardly  be  classed  with  those  so  far  under  consideration  since 
they  are  not  based  on  the  condensation  of  ethine. 

(1)  N=(6)CH  HN—  C=O         HN—  C=O 

(2)  HC     (5)C—  NN(7)    HO     C—  NH  O=C    C—  NH 

6H(8)  <k  6H 

(3)  N_(4)c—  N    (9)     HN-C—  N         HN-C—  N         HN—  C—  NH 

Purin  Base,  6,  oxypurin          2,  6,  dioxypurin        2,  6,  8  trioxypurin 

hypoxanthin,  xanthin,  Uric  acid, 

C6H4N4.  C6H4N40.  C6H4N4O2.  C0H4fl<O3. 

the  purin  base  of  which  the  others  are  derivatives  does  not 
occur  in  nature,  and,  until  recently  synthesized  in  the  labora- 
tory, was  a  purely  hypothetical  compound. 


96 


OUTLINES    OF   PHYSIOLOGICAL    CHEMISTRY. 


The  bracketed  numbers  on  the  purin  base  are  simply  used 
as  a  convenient  method  of  indicating  which  of  the  central  atoms 
is  oxidized  or  substituted.  Thus  on  speaking  of  2,6  dioxypurin 
we  know  at  once  where  the  oxidation  has  occurred. 

Besides  oxidation  of  the  C  atoms  of  the  purin  base,  the  N 
groups  may  be  methylized.  Among  other  derivatives  are  : 


HN— CO 

OC     C— N-  CH8 

ATT 

UN— C-N 

7,  Methylxanthin. 


HN— CO 

OC     C— N-  CH, 


CH3-  N     C-N 

3,  7,  dimethylxanthin 
(Theobromin). 


CH3-  N-CO 


,-J 

OC 


•?•  CH, 
H 


CHS-  N— C  — 

1,  3,  7  trimethylxanthin 
(Caffein). 


Theobromin  is  the  active  principle  of  tea  and  cocoa  whilst  caf- 
fein  is  the  active  principle  of  coffee. 

Purins. —  Besides  methyl  purins,  amino  purins  are  known. 
Of  these  adenin  and  guanin  are  the  only  ones  that  need  be  men- 
tioned. 


y=Q-  NH,     . 
HC    C— NH 


Adenin,  C6H6Ng 


Guanin,  C0H6N6O 


Of  the  above  compounds  uric  acid  is  the  one  which  natu- 
rally is  of  the  most  interest  to  us.  Its  graphic  formula  shows 
that  it  contains  a  central  chain  C  —  C  —  C  and  two  side  chains, 
each  NH  —  CO  —  NH.  If  the  side  chains  were  split  off  and 
H  taken  up  to  resaturate  the  N  atoms  they  would  appear  as 
NH2  -  CO  -  NH2  or  urea. 

Uric  acid  is,  therefore,  closely  related  to  urea,  and  it  was 
formerly  taken  to  represent  an  intermediate  stage  in  the  oxida- 
tion of  proteid  matter  to  urea. 


CYCLIC   COMPOUNDS.  97 

This  view,  however,  is  now  abandoned,  and  it  is  thought 
that  the  small  amount  of  uric  acid  occurring  normally  in  the 
urine  and  the  excess  of  it  in  gouty  conditions  are  derived  largely 
from  the  nucleoproteids,  a  variety  of  proteids  containing  deriva- 
tives of  the  purin  base. 

This  will  be  treated  of  more  fully  in  the  chapter  on  proteids, 
but  one  of  the  theories  (Hofmeister's)  of  urea  and  uric  acid 
production  may  be  discussed  here.  It  seems  the  most  plausible 
of  the  numerous  theories  put  forward,  but  still  it  is  only  a 
theory  and  must  not  be  taken  too  seriously. 

Urea  is  the  main  nitrogenous  product  of  excretion  by  the 
kidneys  in  mammals. 

Urio  add  is  the  main  nitrogenous  product  of  excretion  by 
the  kidneys  in  birds. 

According  to  Hofmeister,  urea  is  an  oxidation  product  of 
glycocoll,  NH3  being  annexed  at  the  same  time. 

CH2NH2.COOH  +  NH3  +  O  =  CO^H^  +  CO2  +  H2O 

Glycocoll.  Urea. 

Although  glycocoll  is  only  found  in  traces  in  the  body  tissue 
it  is  obviously  available  when  needed,  since,  as  we  have 
already  seen,  benzoic  acid  takes  it  up  to  appear  in  the  urine  as 
hippuric  acid. 

It  is  known  that  NH3  is  liberated  kuthe  liver,  although  it 
does  not  leave  the  body  as  such  but  as  urea.  So  NH3  is  available. 

Oxygen  is  certainly  available.  CMp4ation  is  constantly  go- 
ing on  in  the  processes  of  tissue  metabolism.  Glycocoll  there- 
fore may  be  regarded  as  an  immediate  precursor  of  urea,  the 
latter  being  derived  from  it  by  oxidation. 

If  benzoic  acid  is  fed  to  birds  it  does  not  appear  in  the  urine 
as  hippuric  acid  (aminester  of  glycocoll),  but  as  an  aminester  of 
the  diamino  acid,  ornithin. 
7 


98  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 


0 


col  OH] 


|    H;NH-CH2.CH2-CH2.CHNH2-COOH  = 

Benzole  acid  -f  ornithin    = 
O 

-C-NH  -  CH2  -  (CH2)2  .  CHNH2  •  COOH. 
+H20 

Ornithurie  acid. 

It  may  be  then  that  ornithin  is  a  precursor  of  uric  acid  in 
birds,  even  as  glycocoll  is  of  urea  in  mammals.  Like  glycocoll 
it  may  take  up  NH3  and  O  and  lose  H,  at  the  same  time  con- 
densing to  form  a  cyclic  compound. 

)H2NHa  HN-CO 

?H2  00    C— NH 

[2        +2NH3+50a  =  CO  +  7H20+C02* 

[H3  HN-C— NH 

)H 

Ornithin,  CBHlaH2O2  Uric  acid,  C6H4N40, 

The  formation  of  uric  acid  in  birds  is  certainly  a  synthetic 
process,  but  whether  the  synthetic  product  is  ornithin  which  is 
then  oxidized  to  uric  acid,  or  is  the  uric  acid  itself  is  not 
known.  The  theory  here  given  favors  the  former  supposition. 
In  mammals  there  is  no  synthesis  of  uric  acid. 

Pyrimidin  Bases. — By  splitting  off  one  side  of  the  purin  base 
we  get  pyrimidin. 

(1)  N— CH    (6) 

(2)  HO    CH   (5) 

(3)  N=CH    (4) 

Pyrimidin,  C4H4Na  Uracil,  C4H4NS0,       Thymin,  C4H3N2Oa«  CH3 

The  CH  groups  of  pyrimidin  can  be  oxidized  to  uracil,  and 
thymin  is  methyl  uracil. 

Uracil  and  thymin  have  been  found  in  nucleo  proteids. 


CHAPTER  VI. 
THE  PROTEIDS. 

THE  term  protoplasm  employed  to  designate  the  living  matter 
of  plant  and  animal  cells  does  not  mean  a  definite  chemical  sub- 
stance. Any  methods  which  may  be  used  to  determine  the 
chemical  nature  of  protoplasm  results  in  its  destruction  as  living 
matter  so  that  our  ideas  of  it  have  been  derived  from  its  con- 
dition after  death. 

The  compounds  which  are  always  found  under  these  circum- 
stances and  which  are  the  most  characteristic  of  matter  which 
has  been  alive,  are  the  proteids. 

These  occur  in  great  variety  but  their  elementary  composition 
is  fairly  constant,  carbon  52  per  cent.,  hydrogen  7  per  cent., 
nitrogen  16  per  cent.,  oxygen  22  per  cent.,  sulphur  0.5-2  per 
cent. 

Phosphorus  and  iron  are  found  in  some  proteids.  The 
molecule  of  proteid  is  exceedingly  large  when  compared 
with  the  compounds  which  have  already  been  studied,  and 
it  is  impossible  to  give  any  graphic  formula  to  represent 
its  make  up.  On  account  of  this  large  molecule  proteids  in 
solution  are  nondialyzable.  They  will  not  diffuse  through 
parchment. 

There  are  great  differences  in  the  behavior  of  different  pro- 
teids toward  heat,  toward  acid  and  alkaline  solutions,  and  also 
toward  solutions  of  various  salts. 

These  differences  are  the  basis  for  the  classifications  that  are 
made  : 


100 


OUTLINES   OF    PHYSIOLOGICAL    CHEMISTRY. 


A.  Albumens. 
Coagulated  by  heat. 


Globulins. — Soluble  in  dilute  salt 
solutions,  acids,  and  alkalies. 
Precipitated  by  half  saturation 
of  ammonium  sulphate. 

Albumins.  —  Readily  soluble  in 
neutral  fluids,  are  not  precipi- 
tated until  complete  saturation 
by  ammonium  sulphate. 

Albumoses. — Are  precipitated  by 
saturation  with  ammonium  sul- 
phate. 

Peptones. — Not  precipitated  by 
saturation  with  ammonium  sul- 
phate. 

Proteid-like  substance,  resistant 
to  most  reagents,  give  many  of 
the  proteid  reactions. 

Substances  made  up  of  a  proteid 
molecule  combined  with  some 
other  group,  as  the  hemoglobin 
of  the  blood — Hematin  -fglobin 
(an  albumen). 
One  has  to  be  careful  to  distinguish  between  : 

Albumens  and  Albumms. 
Proteids  and  Proteides. 

It  is   unfortunate   that  words  with  different   significations 
should  so  closely  resemble  each  other. 

A.  ALBUMENS. 

1.  The  coagulation  by  heat  or  by  the  action  of  strong  alcohol, 
is  a  characteristic  of  the  albumens.     On  boiling  a  solution  all 


B.  Proteases. 
Not  coagulated  by  heat. 


C.  Albumenoids. 


D.  Proteides. 


THE  PROTEIDS.  101 

the  albumens  are  coagulated,  but  many  of  them  coagulate 
at  considerably  lower  temperatures.  Since  the  temperature 
required  under  similar  conditions  is  constant,  it  is  possible  to 
separate  albumens  by  what  is  called  "  fractional  heat  coagula- 
tion." This  is  accomplished  by  heating  an  albumen  solution 
slowly  until  coagulation  begins ;  maintaining  it  for  a  consider- 
able time  at  that  temperature,  so  that  all  of  that  particular 
albumen  "fraction"  has  time  to  separate  out;  then  filter 
arid  repeat  the  process  at  a  higher  temperature.  In  this 
manner  albumens  may  be  obtained  from  muscle  which  coagulate 
at  47°,  56°  and  63°C. 

The  coagulated  albumen  has  suffered  a  slight  chemical 
change  so  that  it  will  no  longer  or  only  slightly  dissolve  in 
water.  It  gives  however  the  same  proteid  reactions  as  before, 
showing  that  its  proteid  character  is  not  destroyed. 

It  is  sometimes  said  to  be  "  denaturalized." 

2.  Similarly  albumens  may  be  separated  by  fractional  coagu- 
lation  by  alcohol.     Some   are   coagulated  by  dilute  alcohol, 
others  not  until  the  alcohol  is  concentrated. 

3.  A  coagulation  similar  in  many  ways  to  that  produced  by 
heat  may  be  brought  about  in  certain  albumens  by  the  action 
of  enzymes.     For   example  the  clotting  (coagulation)  of  the 
casein  of  milk  by  rennet. 

Precipitation  must  be  distinguished  from  coagulation.  By 
the  former  term  is  meant  the  separation  of  a  proteid  from  its 
solution  because  of  the  addition  of  certain  salts  or  acids,  in  the 
presence  of  which  the  proteid  is  insoluble,  but  without  under- 
going alteration  of  its  chemical  character  or  properties.  The 
albumens  are  precipitated  by  saturating  the  fluid  in  which  they 
are  dissolved  with  ammonium  sulphate.  This  is  called  salting 
out.  The  process  does  not  injure  them  in  any  way,  they  are  not 
denaturalized  since  they  readily  dissolve  again  on  removing  the 


102 


OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 


excess  of  ammonium  sulphate,  so  it  is  a  valuable  method  for 
isolating  them.  Other  salts,  sodium  chloride,  zinc  sulphate, 
etc.,  may  be  used,  but  ammonium  sulphate  gives  the  best 
results.  It  ought  to  be  mentioned,  however,  that  alcohol  first 
precipitates  and  then  coagulates  albumens  after  some  time  has 
elapsed,  so  that  if  the  alcohol  is  filtered  off  quickly  the  albumen 
can  be  redissolved.  We  may  distinguish  : 

1.  Heat  —  coagulates  at  once. 

2.  Alcohol — precipitates  at  once  and  coagulates  later. 

3.  Salts — precipitate  but  do  not  coagulate. 
Albumens  are  divided  into  two  groups  : 

1.  Globulins  precipitated  by  50  per  cent,  ammonium  sul- 
phate. 

2.  Albumins  precipitated  by  saturated  ammonium  sulphate. 
Those  which  have  been  chiefly  studied  are  the  globulin  and 

albumin  of  blood  serum  and  white  of  egg. 
Their  differences  may  be  tabulated  : 


Distilled  Water. 

Saturated  Sodium 
Chloride. 

Saturated  Magnesium 
Chloride. 

Globulin. 
Albumin. 

Insoluble. 
Soluble. 

Insoluble. 
Soluble. 

Insoluble. 
Soluble. 

Of  the  globulins  three  fractions  have  been  distinguished. 

1.  Fibrinoglobulin  precipitated  by  25  per  cent,  ammonium 
sulphate. 

2.  Euglobulin   precipitated    by  32   per    cent,   ammonium 
sulphate. 

3.  Pseudoglobulin  precipitated  by  50  per  cent,  ammonium 
sulphate. 

The  globulins  are  crystallized  with  great  difficulty,  but  of 
the  albumins  egg  albumin  and  the  serum  albumin  of  the  horse 


THE   PROTEIDS.  103 

can  be  readily  crystallized  by  special  methods,  and  thus  be 
obtained  in  purer  form  than  any  of  the  others  for  analysis. 

B.  PROTEOSES. 

These  are  formed  from  the  albumens  as  intermediate  prod- 
ucts of  hydrolysis. 
Diagram matically : 


+H20    = 


O— H  +  H-O 


Albumen.  Proteose         +       Proteose. 

By  hydrolysis  one  molecule  of  an  albumen  has  been  split  into 
two  molecules  of  a  proteose. 

Hydrolysis  of  albumens  can  be  effected  by  boiling  with  dilute 
acids  or  by  the  action  of  digestive  enzymes. 

Proteoses,  therefore,  have  a  smaller  molecule  than  albumens, 
and  consequently  diffuse  more  rapidly  in  solution.  No  doubt 
this  also  accounts  for  their  not  being  coagulated  by  heat.  The 
larger  the  molecule  the  more  easily  it  is  denaturalized. 

The  basis  for  their  separation  into  albumoses  and  peptones 
is  their  behavior  toward  ammonium  sulphate  (see  table). 

C.  ALBUMENOIDS. 

The  albumenoids  form  the  scaffolding  of  the  body.  They 
are  not  themselves  a  constituent  of  protoplasm,  but  are  derived 
from  albumens  partially  oxidized  by  the  living  protoplasm  of 
cells,  and  thrown  off  to  serve  as  a  framework.  The  various 
kinds  of  connective  tissue  are  albumenoids,  and  being  very 
resistant  to  any  but  the  strongest  reagents  make  very  suitable 
coverings  for  the  individual  cells  (fibrous  tissue),  and  even  for 
the  entire  body  (keratin). 


104         OUTLINES  OF  PHYSIOLOGICAL  CHEMISTEY. 

£>.  PROTEIDES. 
This  group  includes  : 

1.  Glycoproteids.  —  Compounds  of  albumen  loosely  combined 
with  glycosamin  or  other  carbohydrates. 

2.  Hemoglobins.  —  Compounds  of  hematin  with  globin  (an 
albumen). 

3.  The  Nudeoproteids.  —  Compounds  of  nucleinic  acid  with 
albumen. 

Summarizing  the  knowledge  thus  far  gained  we  find  : 

1.  The  albumens. 

2.  Proteoses.  —  Albumens  modified  by  hydrolysis. 

3.  Albumenoids.  —  Albumens  modified  by  body  cells. 

4.  Proteides.  —  Albumens  -f  something  else,  the  albumen 
imparting  the  proteid  character. 

All  these  are  included  under  the  general  term  proteid,  but 
the  albumens  are  obviously  the  corner  stone  of  the  whole  edi- 
fice, so  are  called  "  true  proteids." 

In  speaking,  therefore,  in  the  following  pages  of  the  proteid 
molecule  this  practically  refers  to  the  albumens. 

ULTIMATE  ANALYSIS. 

The  approximate  elementary  constituents  of  proteids  have 
already  been  given.  On  ignition  there  is  always  found  a  small 
amount  of  ash.  This  varies  with  the  kind  and  purity  of  the 
proteid,  but  is  made  up  of  varying  amounts  of  chlorides,  sul- 
phates, phosphates  and  carbonates  of  the  metals  sodium,  potas- 
sium, calcium,  magnesium  and  iron.  Some  of  this  ash  is  min- 
eral matter  merely  mixed  with  the  proteid,  whilst  a  portion  is 
probably  combined.  There  is  reason  to  doubt  that  a  truly  ash- 
free  proteid  has  ever  been  obtained. 

Many  attempts  have  been  made  to  determine  the  molecular 
weight  of  albumen  and  other  proteids  by  means  of  ultimate 


THE    PROTEEDS.  105 

analysis,  and  by  determination  of  the  osmotic  pressure  of  their 
solutions. 

No  accurate  figures  have  yet  been  obtained,  but  it  is  certain 
that  the  molecule  is  very  large,  that  there  is  great  variation  in 
its  size  and  that  it  decreases  with  the  progress  of  hydrolysis,  so 
that  albumoses  and  peptones  have  a  much  smaller  molecule 
than  the  albumens.  Some  attempts  have  been  made  to  arrive 
at  a  structural  formula  for  the  comparatively  simple  peptones, 
but  even  these  are  so  extremely  complex  that  this  has  not  yet 
been  accomplished. 

Ultimate  analysis  of  proteids  therefore  has  been  practically 
abandoned,  but  by  hydrolyzing  or  oxidizing  the  entire  molecule 
of  a  proteid  it  can  be  split  up  into  fragments  of  a  simple 
nature,  whose  constitution  is  known,  and  it  is  possible  that  by 
a  study  of  these  fragments  the  manner  in  which  they  are  com- 
bined to  form  the  proteid  molecule  may  be  learned. 

Oxidation  by  means  of  potassium  permanganate  or  other 
oxidizing  agents  is  unsatisfactory  because  : 

1.  The  oxidizing  process  cannot  be  accurately  regulated  so 
that  results  are  not  constant. 

2.  The  fragments  so  obtained  probably  do  not  exist  pre- 
formed as  such  in  the  original  molecule. 

Hydrolysis,  effected  by  means  of  boiling  with  dilute  mineral 
acids,  or  by  treating  with  digestive  enzymes,  such  as  trypsin, 
at  body  temperature,  is  much  more  satisfactory  because : 

1.  The  process  can  be  accurately  regulated. 

2.  The  fragments  obtained  probably  exist  preformed  as  such 
in  the  original  molecule. 

These  fragments  combined  together  go  to  build  up  the  pro- 
teid molecule,  so  they  are  called  its  nuclei. 

The  object  is  to  get  out  the  nuclei  as  nearly  intact  as  possible. 
It  has  been  said  that  albumens  on  hydrolysis  yield  the  proteoses 


106  OUTLINES  OF   PHYSIOLOGICAL   CHEMISTEY. 

as  intermediate  products.  The  proteoses  are  called  interme- 
diate products  because,  on  carrying  on  the  hydrolysis  still 
further,  they  can  be  split  up  into  the  comparatively  simple 
nuclei. 

Proteid  +  n(H2O)  ==  Proteoses. 

Proteoses  -f  n(H2O)  =  Nuclei. 

We  may  now  briefly  consider : 

1.  Products  of  hydrolysis. 

2.  Products  of  oxidation. 

3.  Products  of  bacterial  action. 

4.  Products  of  body  cells. 

1.  PRODUCTS  OF  HYDROLYSIS. 

Proteids  on  hydrolysis  have  been  found  to  yield  the  follow- 
ing list  of  nuclei,  though  not  all  of  them  are  found  in  all 
proteids.  The  principal  ones  only  are  given. 

A.  Monoamino  Acids. 

1.  Aminoacetic  acid  (Glycocoll),  CH2NH2 .  COOH. 

2.  Aminopropionic  acid  (Alanin  C3),  CH3 .  CHNH2 .  COOH. 

3.  a  aminocaproic  acid  (Leucin  C6), 

CH3 .  (CH2)3 .  CHNH2 .  COOH. 

B.  Amino  Diacids. 

4.  Amino    succinic    acid    (Asparaginic    acid   C4),  COOH.- 
CHNH2.CH2.COOH. 

5.  Aminoglutaric  acid  (Glutamic  acid  C5),  COOH.CHNH2  - 
(CH2)2.COOH. 

C.  Diamino  Adds. 

6.  Diamino  acetic  acid,  CH(NH2)2.COOH. 

7.  a,  S,  diamino  valerianic  acid    (Ornithin    C5), 
(CH2)2.CHNH2.COOH. 


THE   PROTEIDS.  107 


8.  a,  e,  diamino  caproic  acid  (Lysin  C6), 


CHNH2.COOH. 


D.  Amino  hexose. 

9.  Glycosamin  (C6)  CHO.CHNH2.(CHOH)3.CH2OH. 

E.  IsocydiG  compounds. 

1 0.  Phenylaminopropionic  acid  (Phenylalanin  C9),  C6H5.CH2.- 
CHNH2.COOH. 

11.  Paraoxyphenylaminopropionic  acid  (Tyrosin  C9),  C6H4- 
(OH),  .(CH2.CHNH2.COOH). 

F.  Heterocydic  Compounds. 

12.  Skatol  ammo  acetic  acid.     (Tryptophan.) 

/\ prr 

!    I    f\* 

I       I       I   XCHNHa- COOH 
NH 

G.  Unknown  Composition. 

13.  Histidin,  C6H9N3O2. 

H.  Sulphur  Compounds. 

14.  a   amino    {3    thio    propionic    acid    (cystein)    CH2SH.- 
CHNH2.COOH. 

All  the  above  are  amino  acids  with  the  exception  of  glyco- 
samin  (amino  aldehyde),  but  there  is  another  exception  of  con- 
siderable importance. 

15.  Guanidin,  CNH(NH2)2. 

Guanidin  occurs  in  combination  with  ornithin  to  form  arginin 
with  loss  of  NH3,  so  is  not  split  off  on  hydrolysis.  Arginin  is 
found  as  the  nucleus  but  is  in  reality  a  double  (binary)  com- 
pound, Guanidin  -f  ornithin. 

Two  points  may  be  noted. 

1.  The  nuclei  all  contain  nitrogen. 


108  OUTLINES   OF  PHYSIOLOGICAL   CHEMISTRY. 

2.  The  NH2  is  always  on  the  C  next  to  the  COOH  group, 
i.  e.j  the  nuclei  are  alpha  amino  acids. 

II.  PRODUCTS  OF  OXIDATION. 

Oxidation  carries  the  decomposition  of  the  proteid  molecule 
much  further  than  hydrolysis,  oxalic  acid  and  gases  CO2,  NH3, 
N  and  H2O  being  among  the  final  products.  Intermediate  prod- 
ucts are  more  or  less  complex  oxycids  about  which  not  much  is 
known.  The  point  to  be  grasped  here  is  that  oxidation  attacks 
the  individual  nuclei,  even  though  they  may  be  still  attached 
to  the  main  molecule,  whilst  hydrolysis  simply  splits  up  the 
main  molecule,  leaving  the  nuclei  intact. 

III.  PRODUCTS  OF  THE  ACTION  OF  BACTERIA. 
A  third  method  of  attacking  the  proteid  molecule  is  by 
means  of  bacteria.  Many  bacteria  can  hydrolyze  proteids, 
e.  g.,  liquefaction  of  gelatin  or  blood  serum,  but  their  action 
does  not  stop  here.  They  have  a  way  of  splitting  off  the  CO2 
of  the  acid  group  from  the  amino  acids,  often  leaving  the  rest 
of  the  nucleus  intact,  for  a  time  at  any  rate.  Ornithin  and 
lysin  are  often  acted  on  in  this  way. 

CH2NH2  •  (CH2)2  •  CHNH2  -  COOH  =  CH2NH2  •  (CH2)2  •  CH2NH2  +  CO, 

Diamino  valerianic  acid  Tetramethylendiamin  (putrescin) 

(ornithin).  -j-  carbon  dioxide. 

CH2NH2  •  (CH2)3  •  CHNH2 .  COOH  =  CH2NH2  •  (CH2)8  •  CH2NH2  +  CO2 

Diamino  caproic  acid  Pentamethylendiamin  (cadaverin) 

(lysin).  +  carbon  dioxide. 

These  and  many  others  formed  in  a  similar  way  from 
monoamino  acids  are  the  bases  which  we  so  often  read  about  as 
being  products  of  putrefaction. 

Cadaverin  and  putrescin  now  suggest  more  to  us  than  merely 
something  with  a  bad  smell. 


THE   PROTEIDS. 


109 


The  bacteria  may  then  proceed  to  partially  oxidize  these 
bases,  forming  oxyamins. 

The  bases  and  their  partial  oxidation  products  resulting  from 
the  action  of  bacteria  are  called  ptomains. 

Instead  of  CO2,  bacteria  may  split  off  NH2,  forming  acids 
instead  of  amins.  Finally  the  ptomains  or  other  products  on 
further  bacterial  action  are  oxidized  and  broken  up  into  gases 
and  nitrates.  These  processes  are  carried  on  by  various  groups 
of  bacteria,  a  fresh  group  taking  up  the  work  where  the  action 
of  a  previous  group  ceases,  these  changes  occurring  naturally 
in  both  soil  and  water. 


IV.   PRODUCTS  OF  ACTION  OF  BODY  CELLS. 

Hydrolysis  and  oxidation  go  on  hand  in  hand  in  the  body, 
the  final  products  being  urea,  CO2  and  H2O.  Intermediate 
products  which  do  not  leave  the  body  as  such  are  called  leuco- 
mains. 

The  leucomains  are  analogous  to  the  ptomains. 

Summarized  in  tabular  form  : 


Method. 

Process. 

Intermediate 
Products. 

Final  Products. 

Acids  or 
enzymes. 
Oxidizing 
agents. 
Bacteria. 

Body  cells. 

Hydrolysis. 
Oxidation. 

Hydrolysis  -{- 
Oxidation. 
Hydrolysis  -(- 
Oxidation. 

Xone.1 
Oxyacids. 
Ptomains. 
Leucomains. 

Amino  acids, 
nuclei. 
Oxalic  acid,  gases, 
water. 
Xit  rates,  gases, 
water. 
Urea,  gases,  \vater. 

Or  diagrammatically,  the  numbers  indicating  various  nuclei 
linked  together 

1  The  earlier  intermediate  proteoses  are  not  taken  into  consideration. 


110  OUTLINES    OF    PHYSIOLOGICAL   CHEMISTRY. 


LlriK,          :Lfrikr 


11 


12  11 

Proteid  molecule. 


H20 

<^0            ^0            HsO          .HjO             HsO           tt.0            ^ 

i 

i 

1             : 

t             3 

J 
1 

1 
3              1 

j 

2               1 

1 
1                J 

)            : 

i 

t 

Hydrolysis. 

^5> 
j 

1               8             I 

-<o          —  <o 

p 

1               3               1 
Os 

2          ii           i 

idation.i 

\           i 

—  <o 

J 

HjO 

V    ^    ^/°    H^°    'H^°    ^v0    ^ 

^0 

Y     \ 

V       - 

r 

17 

1 

j 

<o        1 

-<o 

, 

<o 

~^o 

<o 

1                   3 

11                  3                  12                  11                  8                   39 

Hydrolysis  and  oxidation.    Bacteria  and  body  cells. 

Construction  of  the  Proteid  Molecule.  —  We  have  used  the 
symbol  ]  j  j  j  to  designate  the  construction  of  the  proteid 
molecule,  each  of  the  vertical  lines  representing  a  nucleus  and 
the  horizontal  the  links  which  hold  the  nuclei  together.  We 
may  now  consider  the  manner  in  which  the  various  nuclei  are 
probably  combined. 

The  combination  must  occur  in  such  a  way  : 

1.  That  there  is  dehydration,  since  the  nuclei  are  obtained 

1  As  the  chains  become  oxidized  down  the  links  fall  apart  of  themselves. 


THE   PBOTEIDS.  Ill 

by  hydrolysis.     An  OH  group  must  therefore  always  be  con- 
cerned in  the  synthesis 


j\  —  \j  —  :  —  VJ  —  Jtw 

Synthesis.  Hydrolysis. 

2.  That  the  resulting  molecule  is  neither  distinctly  acid  or 
basic.  The  proteid  molecule  is  amphoteric,  slightly  basic  and 
slightly  acid. 

The  first  thing  to  do  is  to  look  for  OH  groups.  Tyrosin  has 
a  phenol  (OH)  group,  which  might  enter  into  the  combination. 

But  proteid  gives  Millon's  reaction  which  is  due  to  a  free 
OH  group  on  an  isocyclic  ring,  so  the  phenol  group  of  ty  rosin 
must  be  free  and  not  in  combination. 

None  of  the  other  amino  acids  possesses  an  alcohol  or  phenol 
group,  but  they  all,  including  tyrosin,  have  a  COOH  group, 
and  the  OH  of  this  must  be  the  one  which  enters  into  combi- 
nation. 

We  may  take  glycocoll  as  a  typical  amino  acid  and  imagine 
that  it  combines  with  itself  to  form  a  complex  : 

1.  Combination  O  =  C  —  C. 

NH2-  CHa 


iO-H-l-H-iCHNH, 


COOH 


CH,'  CO-  CHNH2'  CO'  CHNH2O>  CHNH,..COOH 

But  in  this  way  the  COOH  groups  are  neutralized  whilst  the 
basic  NH2  groups  remain  free,  a  combination  which  would  lead 
to  a  strongly  basic  character  for  the  compound  molecule. 

In  order  to  preserve  the  weak  amphoteric  reaction  we  must 
suppose  that  the  NH2  groups  enter  into  the  reaction  and  are 


112  OUTLINES  OF   PHYSIOLOGICAL   CHEMISTRY. 

neutralized  as  well  as  the  COOH  groups.     In  this  way  we  can 
build  up  the  complex  as  follows  : 
2.  Combination  OC  —  N. 

HN2-  CHa 


OC-[o^+HJ_NH 
CH2 

oc— i"  o— H+H"]— NH 


COOH 
=H2N-  CH-  C0«  NH.  CH-  CO-  NH-  OH-  CO-  NH-  CH-  COOH 

At  one  end  there  is  the  basic  NH2  and  at  the  other  the  acid 
COOH,  so  that  the  acid  and  basic  qualities  are  precisely  the 
same  as  in  the  original  nuclei,  and  remain  the  same,  no  matter 
what  the  size  of  the  complex  may  be. 

This  constitutes  a  glycocoll  chain,  but  remembering  that  our 
nuclei  are  alpha  amino  acids,  R  —  CHNH2.COOH,  we  can 
substitute  any  of  them  instead  of  glycocoll,  and  in  this  way 
build  up  a  part  of  the  proteid  complex  as  follows  : 

OH:H  OHIH  OHH 

H2N-  CH-  CO— ^NH-  CH-  CO— ;NH-  CH-  CO— NH-  CH-  COOH 

I —  I 


(CH2)2  (CH,), 

CH,  C6H4(OH)  COOH  CH2NH2 

Leucin.  Tyrosin.       Glutamic  acid.  Lysin. 

The  dotted   lines  show  where  combination  took   place  and 
where  splitting  would  occur  on  hydrolysis. 

1.  Hydrolysis. — The  nuclei  are  split  off  as  such. 

2.  Oxidation. — The  side  chains  may  be  supposed  to  become 
oxidized  down  until  we  get 


THE   PROTEIDS.  113 

H3N-  CH-  CO-NH-  CH-  CO- NH-  OH-  CO— NH-  CH-  COOH 

COOH  COOH  COOH  COOH 

The  next  step  would  be  to  split  off  CO2  and  oxidize  the  CH 
groups  of  the  main  chain  into 

H,N-  CO-  CO-  NH-  CO-  CO-  NH-  CO-  CO-  NH-  CO-  COOH 
But  such  a  combination  would  be  so  unstable  that  it  would 
hydrolyze  of  itself,  without  any  stimulus  in  the  shape  of  a 
catalyzer   such  as  a  mineral  acid  or  trypsin,  into  (CONH2.- 
COOH)n  oxalamid. 

Oxalamid  again  is  very  unstable  and  would  of  itself  hydrolyze 
to  oxalic  acid,  COOH.COOH  and  NH3. 

Oxalic  acid,  CO2  and  NH3  are  among  the  chief  products  of 
oxidation  by  potassium  permanganate.  The  fact  helps  to 
support  the  theory. 

3.  Hydrolysis  +  oxidation  as  in  the  body. 
Supposing  the  side  chains  oxidized  down  to 
OHPH  OHH  OH;H 

H2N  •  CH  -  co— pra  •  CH  •  co— jNH  -  CH  -  co— JNH  •  CH  -  COOH 

COOH  COOH  COOH  COOH 

If  hydrolysis  occurs  at  this  point,  we  get  (COOH.CHNH2.- 
COOH)n  or  amino  malonic  acid. 

But  this  is  very  unstable,  being  easily,  by  slight  warming 
even,  split  up  into  glycocoll,  CH2NH2.COOH,  and  CO2. 

As  already  mentioned  glycocoll  is  very  likely  the  immediate 
precursor  of  urea. 

There  are  other  arguments  which  can  be  used  in  support  of 
this  theory,  but  they  need  not  be  discussed  here.  It  must  not, 
however,  be  forgotten  that  this  is  still  a  theory.  There  is  no 
actual  proof  that  the  molecule  is  constructed  in  this  way. 

Defects  of  Hydrolysis. — Hydrolysis  certainly  affords  a  better 
insight  into  the  make-up  of  the  proteid  molecule  than  oxidation, 
but  even  hydrolysis  is  not  perfect. 
8 


114  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

If  carried  out  by  means  of  boiling  with  acids,  certain  dark 
colored  condensation  products  are  afforded,  so  called  melanoidins, 
which  certainly  do  not  exist  as  such  in  the  proteid  molecule,  and 
in  the  formation  of  which  some  of  the  nuclei  must  be  concerned, 
so  to  this  extent  are  lost  for  observation. 

On  digestion  with  trypsin  melanoidins  are  not  formed,  but 
some  of  the  nuclei  may  undergo  changes. 

Taking  the  nucleus  represented  by  the  indol  ring  for  example, 


N/V 

NH 

It  is  probable,  for  reasons  given  later,  that  this  exists  in  the 
proteid  molecule  as  tryptophau.  As  hydrolysis  proceeds  the 
fluid  gives  a  pinkish  color  on  treating  with  chlorine  or  bromine 
water,  showing  the  presence  of  free  tryptophan.  J3ut  before 
the  hydrolytic  process  is  complete  the  tryptophan  reactions  are 
no  longer  given.  The  ring 


'-'•»„ 


is  still  there  but  no  longer  as  tryptophan.     It  may  appear  as 


-7CH, 

it  XCH2NH2 
NH 

skatol  methylamin,  CO2  being  lost,  or  in  other  forms.  Again 
on  hydrolysis  of  proteids  either  by  acids  or  trypsin  NH3  is 
given  off.  This  is  probably  amid  N  driven  off  from  the  amino- 
diacids.  Whatever  its  origin,  it  indicates  something  which  is 
lost  for  observation. 


X 

THE   PROTEIDS.  115 

As  an  example  of  the  different  forms  which  a  nucleus  may 
assume  according  to  the  way  the  proteid  is  treated  tyrosin  may 
be  taken. 

1.  Treated  with  acids,  it  appears  as  tyrosin, 

6" 

CHa-CHNHa-COOH 

and  this  is  probably  the  form  in  which  it  exists  in  the  proteid 
molecule. 

2.  With  trypsin  some  of  the  tyrosin  may  lose  CO2  and  appear 
as  paraoxyphenylethylamin, 


3Ha-CHaNH2 

3.  "With  bacteria  NH3  may  be  lost,  and  it  appears  as  para- 
oxyphenylpropionic  acid, 

)H 


COOH 


CH2-CH2- 


4.  On  oxidation  it  may  appear  as  phenol  or  cresol. 

5.  On  fusing  dry  proteid  with  KOH  there  is  condensation 
and  indol  or  skatol  is  formed. 

CH, 

L         +°     =  f    1     I    +<XV+HIO 
/? 

NHa      COOH 

Tyrosin. 

This  shows  clearly  how  close  are  the  relations  between  tyro- 
sin and  indol,  but  the  balance  of  evidence  is  in  favor  of  there 


116  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTKY. 

being  two  distinct  nuclei  in  the  proteid  molecule,  one  as  tyro- 
sin  and  the  other  as  tryptophan. 

TESTS  FOB  PROTEIDS. 

A.  Color  Tests.  The  color  reactions  which  characterize  the 
proteids  are  due  to  certain  groups  which  they  contain  and  not 
to  the  molecule  as  a  whole. 

1.  Xanthoproteic  reaction  (p.  78)  is  given  by  all  proteids. 
It  indicates  the  presence  of  a  benzene  ring.     Either  tyrosin, 
phenylalanin  or  tryptophan  afford  this  reaction. 

2.  Millon's  reaction  (p.  77)  is  afforded  by  the  phenol  (OH) 
group  of  the  tyrosin  nucleus. 

About  equal  quantities  of  Millon's  reagent  and  the  proteid 
solution  are  mixed  and  warmed  to  about  45°  C.  If  allowed  to 
stand  for  a  few  minutes  the  red  color  appears. 

3.  Adamkievicz  reaction   (p.  94)  is  due  to  the  tryptophan 
group. 

4.  Molisctts  reaction  (p.  90)  is  due  to  the  carbohydrate  group. 
Note. — Proteid  does  not  reduce  Fehling's  solution,  so  the 

aldehyde  group  of  the  glycosamin  is  probably  not  free  but 
forms  the  link  which  binds  the  glycosamin  to  the  proteid.  (See 
disaccharides,  p.  50.) 

5.  Biuret  reaction  (p.  60)  is  due  to  special  combinations  of 
CO  groups,  together  with  at  least  one  free  NH2  group.     Such 
combinations  are  afforded  by  the  nuclei  when  they  are  linked 
together  to  form  complexes,  but  not  by  the  individual  nuclei  as 
such.     After  complete  hydrolysis  the  biuret  test  is  no  longer 
given,  and  in  digestion   experiments  this  test  is  applied  to 
determine  if  the  hydrolysis  is  complete  or  not. 

For  this  purpose  the  first  four  tests  would  obviously  be 
unsuitable  since  the  substances  which  afford  them  as  such 
would  still  be  present. 


THE   PROTEIDS.  117 

It  is  true  the  tryptophan  disappears,  but  not  at  any  definite 
point. 

B.  Alkaloid  Reagents.  —  The  proteids  are  very  complex 
nitrogenous  bases  and  are  precipitated  by  a  number  of  reagents 
which  also  precipitate  certain  simple  nitrogenous  bases  called 
the  alkaloids.  For  this  reason  the  term  alkaloid  reagents  is 
applied  to  them.  It  is  probably  the  diamino  acids  in  the  pro- 
teid  which  give  the  basis  for  these  reactions.  The  precipitation 
is  due  to  chemical  reaction,  and  is  not  analogous  to  precipitation 
by  salting  out,  or  to  coagulation  by  heat  or  alcohol. 

The  most  important  of  these  reagents  are  : 

1.  Phosphotungstic  acid. 

2.  Phosphomolybdic  acid. 

3.  Mercury-potassium  iodide. 

4.  Trichloracetic  acid. 

5.  Picric  acid. 

NITROGEN  OF  THE  PROTEID  MOLECULE. 

The  nitrogen  which  is  the  most  conspicuous  and  character- 
istic element  in  proteid  is  found,  not  in  one  or  two  groups  only, 
but  in  practically  all  of  the  nuclei,  so  that  the  peculiar  nutritive 
properties  of  proteid  are  not  given  by  one  or  two  groups  which 
overshadow  the  rest.  Of  the  N  about  90  per  cent,  on  an 
average  is  in  the  form  of  amino  acids  (stable  N)  but  the 
remaining  10  per  cent,  is  amid  (ammonia)  N  (p.  61). 

It  is  customary  to  divide  the  N  (of  the  hydrolytic  cleavage 
products)  into  three  parts. 

(a)  Amid  or  ammonia  N.  Distilled  over  on  boiling  with 
MgO  (alkaline  base)  and  the  N  of  the  distillate  estimated. 

(6)  Acid  N,  i.  e.,  N  of  monoamino  acids. 

(c)  Basic  N,  i.  e.,  N  of  diamino  acids. 

From  the  residue  of  (a)  the  diamino  acids  are  precipitated 


118  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

by  a  nitrogen  free  alkaloid  precipitant  such  as  phosphotungstic 
acid,  filtered,  and  the  amount  of  N  in  the  filtrate,  acid  N,  and 
precipitate,  basic  N,  respectively  estimated.  A  fourth  determi- 
nation of  the  total  N  in  the  proteid  can  be  made  and  the 
percentages  of  each  kind  of  N  arrived  at. 

Such  a  determination  might  come  out  as  follows : 

Proteid.     Total  N  100. 

I 

Amid  N  Acid  N  Basic  N 


For  the  following  proteids  the  proportions  have  been  found 
to  be 


Amid  NH3 

Acid 

Basic 

Nitrogen. 

Nitrogen. 

Nitrogen. 

Crystallized  egg  albumen. 
Hemoglobin. 

8ft 

6 

68  % 
65 

22  % 

24 

Casein. 

13 

76 

11 

"We  already  know  how  the  amino  N  comes  in,  but  the  ques- 
tion arises :  How  is  the  amid  N  combined  ?  Probably  the 
COOH  group  of  the  amino  acid  enters  into  combination  with 
the  proteid  molecules. 

E_L 

Proteid  molecule.      Nucleus. 

So  that  on  most  of  the  amino  acids  no  amid  N  could  exist,  but 
some  of  them  are  amino  diacids  and  here  there  might  be  a 
spare  COOH  group  for  amid  N. 


E C-  CHNH2.  CH2.  COOH+NH8 

Proteid  molecule.  Asparaginic  acid. 


„•  CH2-  CONH2+H2O 


Proteid  molecule.  Asparaginic  amid. 


THE  PROTEIDS.  119 

CONSTITUENTS  OF  THE  PROTEID  MOLECULE. 

We  can  now  proceed  to  consider  these  in  detail,  but  before 
doing  so  it  must  be  clearly  understood  that  the  nuclei  here  dis- 
cussed are  not  found  free  as  such  in  fresh  animal  organs  or 
tissues,  or  only  to  a  limited  extent.  We  are  simply  dealing 
with  products  of  hydrolytic  action  on  tissue  or  proteids  prepared 
from  it. 

In  normal  tissues  the  amount  of  proteid  being  broken  down 
at  any  given  moment  of  time  is  so  small  that  the  presence  of 
products  intermediate  between  proteid  and  urea  can  very  rarely 
be  demonstrated. 

A.  Monoamino  Acids. 

The  monoamino  acids  have  an  amphoteric  reaction.  They 
are  acid  by  virtue  of  their  COOH  group  and  at  the  same  time 
basic  by  virtue  of  their  NH2  group.  Since  they  are  by  far  the 
most  abundant  constituents  of  the  proteid  molecule  they  impart 
this  characteristic  to  it. 

The  proteid  molecule,  therefore,  is  both  acid  and  basic. 

3.  Leucin  (isobutylamino  acetic  acid)  is  the  most  important 
of  all  the  nuclei,  being  found  in  all  proteids  in  varying  per- 
centages up  to  40  per  cent,  or  50  per  cent.  This  being  so  it 
is  well  to  know  how  it  can  be  obtained  from  among  the  products 
of  hydrolysis. 

Precipitate  the  solution  with  basic  lead  acetate,  to  remove 
the  proteid.  Filter  and  remove  the  excess  of  lead  acetate  by 
passing  H2S  through.  The  black  PbS  precipitate  is  filtered 
off  and  the  nitrate  evaporated  to  small  bulk.  The  process  is 
repeated  and  after  again  evaporating  to  small  bulk  on  the  water 
bath,  keep  at  room  temperature  for  two  or  three  days  in  an 
open  porcelain  dish.  As  the  fluid  gradually  evaporates  the 
leucin  crystallizes  out.  Under  the  microscope  xhe  crystals 
appear  as  globules  with  a  radially  striated  appearance. 


120  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

1.  Glycocoll  (amino  acetic  acid). — Next  in  importance  of  the 
monoamino  acids  may  be  ranked  glycocoll,  not  so  much  on 
account  of  its  relative  abundance  among  the  products  of  artificial 
hydrolysis  as  the  fact  that  it  is  probably  a  constant  intermediate 
oxidation  product  of  animal  metabolism,  the  immediate  pre- 
cursor of  urea. 

Glycocoll  is  found,  as  a  nucleus,  very  sparingly  in  true  proteids 
and  may  often  be  wanting  altogether,  but  in  the  albumenoids, 
gelatin,  collagen,  is  relatively  abundant. 

This  is  significant  since  the  albumenoids  are  regarded  as 
partially  oxidized  proteid. 

2.  Alanin  (amino  propionic  acid)  is  only  sparingly  present 
as  such  but  occurs  in  considerable  quantities  in  combination 
with  phenol  to  form  tyrosin  and  with  indol  to  form  tryptophan. 
Tyrosin  and  tryptophan  might,  therefore,  be  ranked  with  arginin 
and  regarded  as  binary  compounds.     But  the  alanin  is  very 
firmly  attached  to  them  and  cannot  be  separated  as  such  even 
by  drastic   methods  so  it  is  better  to  consider   tyrosin    and 
tryptophan  as  definite  single  nuclei. 

B.  Amino  Diacids. 

5.  Glutamic  acid  occurs  more  frequently  than 
4.  Asparaginic  Add. — It  is  to  one  of  the  COOH  groups  of 
diacids  that  the  amid  N  of  the  proteid  molecule  is  probably 
attached,  although  there  is  no  direct  proof  of  this.  It  is  signif- 
icant, however,  to  find  that  casein,  which  contains  so  much 
amid  N  (13  per  cent,  of  the  total  N),  also  contains  a  large 
amount  of  glutamic  acid  (10  per  cent.). 

EEACTIONS. 

The  monoamino  acids  and  diacids,  products  of  hydrolysis, 
can  be  benzoylized  ;  the  resulting  benzoyl  compounds  having 
different  solubilities  which  enable  the  chemist  to  separate  them 


THE   PROTEIDS.  121 

with  a  considerable  degree  of  sharpness.  The  solution  to  be 
benzoylized  should  be  made  strongly  alkaline  with  10  per  cent. 
NaOH,  benzoyl  chloride  added  gradually  in  small  quantities 
with  continuous  shaking. 

Or  the  acids  may  be  converted  into  their  ethyl  esters  and 
distilled  over  "  in  vacuo."  Since  these  esters  have  different 
boiling  points  they  may  be  separated  by  fractional  distillation. 
There  is  some  difficulty  in  keeping  the  pressure  at  the  low 
point,  4-12  mm.,  required  to  prevent  decomposition,  but,  prop- 
erly carried  out,  the  method  gives  excellent  results. 

C.  Diamino  adds. 

The  simplest  of  these  is  6,  diamino  acetic  acid,  which  has 
been  found  only  once  as  a  product  of  the  hydrolysis  as  casein. 

7.  Ornithin  a,  8,  diamino  valerianic  acid,  is  of  much  greater 
interest.  It  is  found  among  hydrolytic  cleavage  products 
combined  with  guanidin  to  form  arginin.  The  series  of  steps 
by  which  the  structure  of  arginin  was  determined  forms  an  in- 
teresting chapter  in  physiological  chemistry. 

An  already  mentioned  ordinary  hydrolysis  by  acids  or  trypsin 
does  not  split  arginin,  but  by  more  drastic  hydrolytic  processes, 
such  as  boiling  with  baryta  water,  the  molecule  is  split  up  into 
urea  and  ornithin. 

NH2 

C=NH 


—  CH2-  (CH2)2-  CHNH2-  COOH  +  H2O 

Arginin. 


CH2NH2-  (CH2)2-  CHNH2-  COOH. 

Ornithin. 


122  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

Among  the  oxidation  products  of  arginin  are  : 
NH2 


CH2NH2 

NH—  CH2  and          (CH2)2 


COOH 

Guanidin  butyric  acid.  Putrescin  (by  bacteria). 

Guanidin  butyric  acid  can  be  further  oxidized  to  : 
COOH-  CH2-  CH2.  COOH 

Succinic  acid. 

Succinic  acid  occurs  in  small  quantities  in  beer  among  the 
products  of  alcoholic  fermentation. 

It  had  until  recently  been  supposed  that  the  succinic  acid 
was  derived  from  the  carbohydrates  of  the  malt,  but  it  seems 
more  probable  that  it  is  an  oxidation  product  of  arginin,  and 
therefore  derived  from  the  malt  proteid. 

Arginin  is  found  as  a  product  of  hydrolysis  in  all  proteids, 
being  the  most  abundant  of  the  basic  substances.  It  is,  espe- 
cially prominent  in  the  proteid  of  certain  seeds  and  in  the  pro- 
tamins. 

8.  Lysin  has  been  found  in  seedlings,  as  a  product  of  tryptic 
digestion  of  fibrin,  and  in  certain  kinds  of  cheese.  Cadaverin, 
which  stands  in  the  same  relation  to  lysin  as  putrescin  does  to 
ornithin,  has  also  been  found  in  cheese,  probably  limburger. 
Both  cadaverin  and  putrescin  are  constant  products  of  putre- 
faction. 

13.  Histidin  of  unknown  constitution  also  occurs  among  the 
cleavage  products  of  certain  proteids,  more  particularly  of  some 
protamins.  The  protamins  will  be  discussed  later. 

Arginin.  Lysin.  Histidin. 

Edestin  proteid  from  hemp  seeds,  11.07%  1.3%  1.17% 

Proteid  from  pine  seeds,  10.9  .25  .62 


THE   PROTEIDS.  123 

These  three  basic  substances  : 

Arginin        C^TSflv 
Lysin  C^N/X, 

Histidin        CJBiffflv 

have  been  grouped  together  to  form  the  hexon  bases  of  Kossel, 
since  each  contains  six  C  atoins.  Kossel  has  tried  to  show 
that  they  are  closely  related  to  each  other  and  points  out  the 
probability  that  they  may  be  oxidized  to  hexoses  in  the  body, 
suggesting  that  in  this  way  sugar  may  be  derived  from  proteid. 
In  this,  however,  he  seems  to  be  mistaken  since,  with  the 
exception  of  lysin,  their  constitutions  are  entirely  different  from 
the  normal  saturated  C  chains  of  the  hexoses. 

Arginin  contains  five  C  atoms  united  to  a  sixth  by  means  of 
N,  whilst  histidin  contains  too  few  H  atoms  to  form  a  normal 
saturated  chain.  It  must  either  be  an  unsaturated  compound,  or, 
as  seems  more  probable  from  recent  researches,  a  cyclic  com- 
pound allied  to  the  pyrimidins.  As  a  matter  of  convenience 
however  the  term  hexon  bases  may  be  retained. 

The  hexon  bases  are  precipitated  from  acid  solutions  by  the 
alkaloid  reagents,  and  by  this  means  can  be  separated  as  a 
group  from  the  monoamino  acids.  The  methods  for  isolating 
and  separating  them  from  each  other  are  too  complicated  to  be 
given  here. 

D.   Carbohydrate  Nucleus,  Glycosamln. 

In  speaking  of  the  carbohydrate  nucleus  of  the  proteid  mole- 
cule it  must  be  clearly  understood  that  this  is  not  the  only  form 
in  which  carbohydrates  exist  in  the  animal  body.  Glycogen 
is  stored  up  in  the  liver  and  glucose  as  such  occurs  in  the  tis- 
sues apart  from  the  glycosamin  in  combination. 

It  has  long  been  known  that  the  proteids  contain  a  carbohv- 


124  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

drate  nucleus,  since,  among  others,  Molisch's  color  reaction  in- 
dicates the  presence  of  a  carbohydrate. 

Certain  proteids,  such  as  mucin,  have  been  found  to  yield  a 
relatively  large  amount  of  carbohydrates  in  the  earliest  stages 
of  hydrolysis  with  dilute  acids,  parting  with  their  glycosamin 
very  readily. 

These  compounds  called  glycoproteids,  are  distinguished  from 
the  true  proteids  which  yield  their  carbohydrate  group  only  on 
complete  destruction  of  the  proteid  character  of  the  molecule. 

The  carbohydrate  group  most  frequently  found  contains 
nitrogen  (glycosamin)  and  has  in  many  cases  been  proved  to  be 
identical  with  chitosamin,  which  has  been  known  for  a  long 
time  as  the  chief  cleavage  product  of  chitin,  the  chemical  basis 
of  the  skeleton  of  insects  and  crustaceans. 

It  is  probable  that  the  glycosamin  is  not  present  as  such  in 
the  proteid  molecule,  but  occurs  as  a  dissacharide  or  polysac- 
charide,  which  is  broken  down  on  hydrolysis. 

The  decomposition  of  nucleoproteids  from  the  pancreas,  thy- 
mus,  spleen,  etc.,  gives  a  carbohydrate  group  which  has  been 
identified  as  a  true  pentose,  1 -xylose,  and  not  a  lower  homo- 
logue  of  the  amino  sugar  glycosamin. 

Much  of  the  proof  that  a  carbohydrate  group  may  be  derived 
from  a  proteid  is  physiological  rather  than  chemical.  For  in- 
stance, in  diabetes  large  quantities  of  sugar  are  excreted  in  the 
urine  even  though  no  carbohydrate  is  taken  in  the  food,  and 
when  the  disease  has  persisted  long  enough  to  remove  all  the 
stored  carbohydrate  and  a  large  portion  of  the  fat.  Again,  if 
an  animal  is  starved  until  the  liver  is  glycogen  free  and  is  then 
fed  a  pure  proteid,  glycogen  will  again  appear  in  the  liver. 

These  instances,  however,  only  show  that  carbohydrates  can  be 
derived  from  proteid,  but  the  chemist  by  decomposing  a  pro- 
teid, egg  albumin,  for  instance,  and  finding  glycosamin  among 


THE   PROTEIDS.  125 

the  cleavage  products  is  able  to  demonstrate  its  presence  as  a 
definite  nucleus.  There  is  no  evidence  to  show  that  animal 
metabolism  can  build  up  sugars  from  the  other  constituents  of 
proteids. 

AROMATIC  NUCLEI. 
E.  Isocydic  Nuclei. 

10,  Phenylalanin  and  11,  Tyrosin. 

These  two  closely  related  compounds  are  always  found 
among  the  hydrolytic  cleavage  products  of  true  proteids.  Gel- 
atin, an  albumenoid,  gives  Millon's  reaction  though  as  yet  no 
tyrosin  has  been  obtained  from  it.  Gelatin  yields  phenylalanin 
on  cleavage,  but  this  does  not  give  Millon's  reaction.  There 
must  therefore,  be  some  phenol  group  in  the  gelatin  other  than 
tyrosin,  or  else  the  tyrosin  is  combined  in  some  peculiar  way 
that  it  cannot  be  obtained  as  such.  Other  albumenoids  are 
very  rich  in  tyrosin,  keratin  sometimes  containing  as  much  as 
4.5  per  cent.  The  amount  of  tyrosin  found  as  a  cleavage  prod- 
uct of  different  proteids  varies  very  widely. 

Egg  albumen,  1-2%  Fibrin,  2-3% 

Plant  albumen,  2  Horn,  3.6-4 

Muscle,  1  Casein,  4 

Tyrosin  separates  out  with  leucin  on  treatment  with  lead 
acetate.  It  is  less  soluble  than  leucin  and  crystallizes  out  first 
in  sheaves  of  needles,  reminding  one  of  bundles  of  wheat. 
Tyrosin  can  be  separated  from  leucin  by  treatment  with  alcohol 
to  which  a  little  ammonia  has  been  added.  In  this  the  tyrosin 
dissolves  but  the  leucin  does  not. 

Piria's  Test.  —  A  drop  or  two  of  concentrated  HJSC^  is 
added  to  the  tyrosin  in  a  watch  glass.  After  allowing  to  stand 
for  half  an  hour  to  form  tyrosin  sulphuric  acid,  dilute  the  acid 
with  water  and  neutralize  with  calcium  carbonate.  The  solu- 
tion is  filtered  from  the  calcium  sulphate  thus  formed  and  a 


126  OUTLINES    OF    PHYSIOLOGICAL   CHEMISTRY. 

drop  of  neutralized  ferric  chloride  added.     A  deep  violet  color 
appears,  probably  the  iron  salt  of  tyrosin  sulphuric  acid. 
Tyrosin  also  gives  Millon's  reaction  as  already  mentioned. 

F.  Heterocyclic  Nucleus. 

12.  Tryptophan  has  only  lately  been  recognized  as  a  nucleus, 
so  requires  a  little  preliminary  explanation. 

On  fusing  proteid  with  KOH,  indol  and  skatol  are  formed. 
A  part  of  these  are  probably  condensation  products  of  tyrosin, 
but  more  indol  and  skatol  are  formed  than  can  be  accounted  for 
in  this  way.  Again  on  decomposition  of  proteid  by  bacteria, 
a  large  quantity  of  indol  and  skatol  may  be  found  among  the 
products. 

The  presence  of  an  indol 


ra 

ring  as  a  nucleus  has  therefore  been  accepted  for  many  years, 
but  until  recently  there  was  no  evidence  to  show  in  what  form 
it  exists  in  the  proteid  molecule. 

The  name  proteinochromogen  or  tryptophan  was  long  since 
adopted  for  the  hydrolytic  cleavage  product  which  affords  a 
pinkish  color  with  bromine  or  chlorine  water. 

It  has  recently  been  found  possible  to  isolate  tryptophan  by 
precipitation  with  mercury  bisulphate  so  that  it  can  be  studied 
in  pure  condition.  This  fact  has  enabled  chemists  not  only  to 
determine  its  constitution  as  skatol  amino  acetic  acid 


COOH 
H 


but  also  to  identify  it  with  the  substance  which  affords  the 
Adamkievicz  reaction  for  proteids  —  violet  color  with  H2SO4 
and  acetic  acid. 


THE    PROTEIDS.  127 

Before  going  further  three  points  must  be  clearly  under- 
stood : 

1.  The  Adarnkievicz  reaction  indicates  tryptophan  in  combi- 
nation in  the  proteid  molecule. 

2.  The  bromine  or  chlorine  water  reaction  is  given  during 
the  progress  of  hydrolysis  and  indicates  free  tryptophan. 

3.  About  the  time  that  hydrolysis  is  complete  the    latter 
reaction   is   no    longer   given.      The   tryptophan   has   disap- 
peared. 

Now  the  intact  proteid  molecule  gives  no  reactions  for  indol 
or  any  of  its  derivatives  except  tryptophan,  so  it  is  supposed 
in  the  light  of  these  recent  discoveries  that  tryptophan  is  the 
form  in  which  the  indol  ring  exists  in  the  proteid  molecule, 
although  tryptophan  itself  is  not  found  as  a  final  product  of 
hydrolysis. 

Like  tyrosin  the  ring  may  appear  in  various  forms  according 
to  the  way  in  which  it  is  treated.  With  trypsin  it  may  appear 
as  skatol  methylamin.  On  partial  oxidation  or  with  bacteria 
as  indol,  skatol,  or  skatol  carbonic  acid,  and  in  the  urine  as 
indoxyl  sulphuric  acid. 

All  these  may  be  regarded  as  derived  from  tryptophan  by 
splitting  off  more  or  less  of  its  side  chain. 

Tryptophan  is  always  called  skatol  amino  acetic  acid  but  if 
we  regard  it  as  indol  amino  propionic  acid  (indolalanin)  its  rela- 
tions to  tyrosin  can  be  much  better  appreciated. 


— ^CH,  •  CHNH2  •  COOH. 


128 


OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 


Tyrosin  (phenol  and  alanin)  may  condense  to  indol  and 
tryptophan  is  indol  and  alanin. 

The  cleavage  products  of  each  are  analogous.  The  alanin, 
which  we  may  call  the  side  chain,  is  attacked,  but  the  ring  is 
unchanged. 


With  trypsiu 
we  may  get 


OH 


Tyrosin  nucleus. 

CH2-  CH2NH8 


Tryptophan  nucleus. 

] CH2-  CH2NH3 


Phenol  ethylamin. 

Indol  ethylamin 
(Skatol  methylamin). 

/                     />  CH2.  COOH 

OH'\/ 

Phenol  acetic  acid. 

/\  1  CH3-  COOH 

\/\/ 

Nil 

Indol  acetic  acid 
(Skatol  carbonic  acid). 

With  bacteria 
or 
oxidation. 

,/\  CHS 

OH\/ 

Methyl  phenol 
(Paracresol). 

CX/"' 

NH 

Methyl  indol 
(Skatol). 

o»0 

Phenol. 

Oj 

NH 

Indol. 

In  the  urine        H08S— O—  |         | 


I         i 


— O— SO3H 


II 


Indoxyl  sulphuric  acid 
(Indican). 


Phenol  sulphuric  acid. 

Indol  is  a  toxic  substance  and  when  absorbed  in  the  intestine 
is  carried  by  the  portal  vein  to  the  liver  where  it  is  oxidized  to 
indoxyl  which  combines  with  sulphuric  acid  to  form  indoxyl 
sulphuric  acid  which  is  not  toxic  and  is  excreted  as  a  potassium 
salt  in  the  urine.  ^ 

/\  II 

— 0— K 


THE   PBOTEIDS.  129 

Skatol  is  rendered  harmless  and  eliminated  in  the  same  way. 
This  synthesis  is  one  of  many  similar  ones  designed  to  protect 
the  organism  from  the  poisonous  effects  of  proteid  decomposi- 
tion products.  Phenol  and  cresol  are  also  eliminated  as  potas- 
sium sulphates. 

The  amount  of  combined  sulphates  in  the  urine  is  a  measure 
of  the  extent  of  intestinal  putrefaction.  The  sulphates  in  urine 
are  grouped  as  mineral  (uncombined)  and  combined,  the  latter 
being  those  in  combination  with  indoxyl  or  some  other  aro- 
matic ring. 

BaCl2  is  added  to  the  urine  and  this  precipitates  the  uncom- 
bined but  not  the  combined  sulphates. 

BaCl2  +  K2SO4  =  BaSO4  +  2KC1. 

The  fluid  is  then  filtered  and  the  filtrate  boiled  with  hydro- 
chloric acid.  This  splits  off  the  indoxyl  or  other  aromatic 
compound  and  the  combined  become  uncombined  sulphates 
which  can  then  be  precipitated  by  BaCl2  and  weighed  as  BaSO4. 

This  method  gives  an  index  to  the  total  amounts  of  aromatic 
products  of  intestinal  putrefaction  which  are  absorbed,  indols, 
phenols,  or  cresols.  A  part  of  these  products  are  excreted  in 
combination  with  glycuronic  acid,  but  the  amounts  are  com- 
paratively insignificant  and  are  ignored  in  making  the  test. 

Clinical  Test  for  indican  alone.  The  urine  is  treated  with  an 
oxidizing  agent  —  concentrated  HC1  containing  a  little  FeCl3 ; 
this  oxidizes  the  indican  with  formation  of  indigo  blue,  which 
is  obtained  by  shaking  out  with  chloroform,  in  which  it  is 
soluble.  The  depth  of  blue  color  in  the  chloroform  solution 
affords  a  rough  estimate  of  the  amount  of  indican  present. 

Indoxyl  will  oxidize  itself  to  indigo  blue  by  taking  up  O 
from  the  air,  but  the  FeCl3  being  an  oxidizing  agent,  hastens 
the  process. 
9 


130  OUTLINES   OF    PHYSIOLOGICAL    CHEMISTRY. 

H.  Sulphur  Compounds. 

The  S  of  the  proteid  molecule  exists  chiefly  as  cystin. 
Cystin  is  a  binary  compound  made  up  of  two  molecules  of 
cystein  ;  analogous  therefore  to  arginin. 


E-S  jH+Hj—  S—  CH2 
TH2  CHNHa    = 

H  COOH 

a  amino,  /3  thiopropionic  acid 
Cystein       +       Cystem 

Since  the  two  molecules  of  cystein  combine  with  loss  of  H2, 
not  of  H2O,  cystiu  is  not  split  up  by  hydrolysis  but  appears  as 
such  among  the  proteids  ;  not  as  the  ultimate  nucleus  cystein. 

To  estimate  the  total  amount  of  S,  the  proteid  is  completely 
oxidized  by  nitric  acid,  BaCl2  added,  and  the  sulphur  weighed 
as  BaSO4. 

On  boiling  some  proteids  with  lead  acetate  in  alkaline  solu- 
tion, black  lead  sulphide,  PbS,  is  quickly  precipitated.  The 
alkali  splits  off  the  S,  which  then  combines  with  the  Pb.  But 
there  is  always  some  sulphur  left  which  cannot  be  precipitated 
in  this  way.  The  former  is  loosely  combined  and  the  latter  is 
in  stable  combination. 

It  was  formerly  supposed  that  the  loosely  combined  S  exists 
in  unoxidized  form  K  —  S  —  H,  and  the  stable  in  oxidized 
form  as  sulphites  or  sulphates,  so  the  S  of  proteids  was  classified 
as  oxidized  and  unoxidized. 

But  there  is  no  evidence  to  show  that  oxidized  S  occurs  in 
the  proteid  molecule.  Sulphites  and  sulphates  are  never  found 
among  the  products  of  hydrolysis.  Moreover  experiments  with 
pure  cystin  have  proved  that  its  S  is  distinctly  stable  and  can 
only  be  partially  precipitated  even  by  prolonged  boiling  with 
alkaline  lead  acetate. 

We  may  conclude,  therefore,  that  the  stable  S  of  the  proteid 


THE   PROTEIDS.  131 

represents  the  cystin,  whilst  the  loosely  combined  must  exist  in 
some  other  form  as  B,  —  S  —  H. 

Just  how  it  exists  is  not  accurately  known,  but  mercaptans, 
-  methyl,  CH3SH,  and  ethyl,  CH3.CH2SH  -  and  thiolactio 
acid,  CH3.CHSH.COOH,  have  been  found  as  cleavage  products 
on  partial  oxidation  of  proteids,  though  they  cannot  be  regarded 
as  definite  nuclei  existing  preformed  in  the  molecule.  In  all 
these  compounds  the  S  occurs  as  E,  —  S  — -  H,  and  may  be  split 
off  by  boiling  with  alkalies. 

Again  a  certain  amount  of  H2S  passes  off  as  gas  during 
hydrolysis,  and  this,  since  the  cystin  is  not  affected,  must  have 
been  combined  in  some  other  form. 

The  proportions  of  loosely  combined  and  stable  S  vary  much 
in  different  proteids,  the  former  being  frequently  absent  alto- 
gether, whilst  some  of  the  albumoses  contain  only  loosely  com- 
bined S. 

From  some  of  the  albumenoids,  the  keratins  particularly, 
large  amounts  of  cystin,  as  well  as  loosely  combined  sulphur, 
have  been  obtained. 

The  close  relation  of  cystin  to  taurin,  a  constituent  of  one  of 
the  bile  acids,  suggests  a  possible  origin  for  the  latter  compound. 

E3H  CH,.S03H 

HE,  CH3NH3 

H 

Cy  stein.  Taurin. 

The  transformation  has  been  accomplished  in  the  laboratory 
as  follows : 

CH2SH  CH2SO3H 

CHXH,    oxidation  by  Bromine  »->•     CHNH, 

COOH  COOH 

Cystein.  Cystein  sulphuric  acid. 


132  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTEY. 

On  heating  cystein  sulphuric  acid  in  a  sealed  tube  CO2  is  split 
off  (so  called  CO2  condensation),  leaving 

CH2S03H 
CH2NHa 

Taurin. 

On  feeding  animals  with  cystin  it  is  found  that  the  amount 
of  taurin  in  the  bile  is  markedly  increased.  Seeing  also  how 
easily  the  change  from  cystin  can  be  effected  artificially  it  is 
considered  probable  that  the  taurin  of  the  bile  is  directly  de- 
rived from  the  cystin  of  the  proteid  molecule. 

Cystin  is  closely  related  to  serin,  a  cleavage  product  of  silk 

fiber. 

CH2OH 

CHNH3 

COOH 
a  amino  /3  oxypropionic  acid.   Serin. 

Silk  fiber  is  an  albumenoid  and  therefore  a  modified  albumen. 
Serin  is  probably  modified  cystein. 

INTERMEDIATE  PRODUCTS  OF  HYDROLYSIS  OR 

PROTEOSES.     ALBUMENS   MODIFIED 

BY  HYDROLYSIS. 

Our  discussion  so  far  has  been  confined  to  the  true  pro- 
teids  or  albumens,  and  their  nuclei,  or  final  products  of  hydro- 
lysis. We  have  already  mentioned,  however,  that  there  are 
certain  intermediate  products,  and  these  may  be  taken  up  more 
in  detail. 

A.  ACID  AND  ALKALI  ALBUMENS. 

On  treating  albumen  with  dilute  acid  or  alkali  it  gradually 
undergoes  a  modification  which  is  not  very  well  understood, 
but  in  all  probability  represents  the  very  earliest  stages  of  hy- 


THE   PROTEIDS.  133 

drolytic  cleavage.  H2S  is  given  off  by  alkali,  NH3  by  acid 
treatment ;  so  there  must,  at  any  rate,  be  a  change  in  the  mole- 
cule of  some  nature. 

The  albumen  in  this  condition  will  act  as  a  base  in  acid  solu- 
tion, combining  with  the  acid  to  form  a  salt.  In  alkaline  solu- 
tion it  acts  as  an  acid,  forming  a  salt  with  an  alkali.  In  either 
case  the  salt  is  soluble,  but  on  neutralizing  the  solution  the 
albumen  is  driven  from  its  combination  and  precipitates  out  as 
a  coagulum,  showing  that  it  is  denaturalized.  On  again  acidi- 
fying or  alkalinizing  the  fluid  the  albumen  again  dissolves  as  a 
salt. 

The  acid  and  alkali  albumens  when  in  solution  are  not  coag- 
ulable  by  heat  but  can  be  easily  salted  out,  resembling  globu- 
lins in  the  latter  respect.  They  are  very  easily  hydrolyzed  by 
boiling  with  dilute  acids  or  by  the  action  of  enzymes. 

Proteid  in  this  condition  may  be  regarded  as  intermediate 
between  albumen  and  the  proteoses. 

Note.  —  It  must  be  understood  that  this  change  takes  place 
very  slowly  in  the  cold,  but  more  rapidly  on  warming  the  solu- 
tion. In  speaking,  therefore,  of  proteids  in  acid  or  alkaline 
solution  it  does  not  necessarily  mean  that  the  proteid  is  in  the 
form  of  acid  or  alkali  albumen. 


Th( 


B.  PROTEOSES. 


ie  intermediate  products  which  are  obtained  when  any 
proteid  is  subjected  to  hydrolytic  cleavage  by  any  method  are 
called  proteoses.  This  is  a  general  term  applied  to  a  large 
number  of  substances  showing  considerable  differences  among 
themselves,  but  which  still  have  enough  of  the  proteid  character 
to  distinguish  them  clearly  from  the  final  products  of  hydrol- 
ysis, i.  e.,  the  nuclei. 


134  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTEY. 

The  proteoses  as  a  group  resemble  the  true  proteids  in  that 
they,  speaking  very  generally,  give  : 

1.  All  or  nearly  all  the  color  reactions  due  to  definite  nuclei. 

2.  The  biuret  test,  implying  that  their  internal  arrangement 
is  similar. 

3.  The  same  chemical  precipitation  reactions  with  alkaloid 
reagents  or  metallic  salts. 

They  differ  from  the  true  proteids  in  that  they : 

1.  Do   not  coagulate  by  heat  or  by  the  action  of  strong 
alcohol  as  a  rule. 

2.  Do  not  as  a  rule  salt  out  so  readily. 

3.  Are  dialyzable  and  therefore  have  a  smaller  molecule. 
They  are  separated  from  coagulable  proteid  in  solution  by 

boiling  and  filtering.  The  filtrate  contains  the  proteoses  only. 
Since  their  chemical  constitutions  are  not  known  they  can 
only  be  grouped  according  to  their  physical  properties,  and 
their  behavior  towards  ammonium  sulphate  is  the  most  conve- 
nient method  of  differentiating  them. 

I.  Albumoses.     Precipitated  by  saturated  ammo- 

nium sulphate. 
Proteoses  < 

II.  Peptones.     Not    precipitated   by   ammonium 

sulphate. 

I.  Albumoses. 

A  great  variety  of  albumoses  has  been  recognized,  but  we 
can  only  attempt  to  deal  with  the  more  important  of  them. 

A.  Primary.     Precipitated    by    50    per    cent. 

ammonium  sulphate  (in  acid  solution). 
Albumoses  « 

B.  Secondary.     Precipitated  by  saturated  ammo- 

nium sulphate. 


THE   PKOTEIDS.  135 

Primary  albumoses  are  subdivided  into  : 

"1.  Heteroalbumose.    Precipitated  by  sat- 
urated neutral  sodium  chloride, 
imary  albumoses  - 

2.  Protalbumose.     Precipitated  by  sat- 
urated acid  sodium  chloride. 

1.  Heteroalbumose  of  all  the  proteoses  is  the  nearest  to  true 
proteids,  being  the  only  one  which  is  nondialyzable  and  pre- 
cipitable  in  weak  alcohol  (32  per  cent.). 

In  some  respects  it  resembles  the  globulins,  being  insoluble 
in  distilled  water,  but  easily  dissolved  on  adding  a  little  salt. 

2.  Protalbumose  is  very  soluble  in  distilled  water,  and  is 
readily  dialyzable,  so  that  its  molecular  weight  must  be  lower 
than  that  of  heteroalbumose. 

It  is  more  soluble  in  dilute  alcohol  than  in  water,  but  begins  to 
precipitate  in  80  per  cent,  alcohol,  although  it  cannot  be  com- 
pletely precipitated  except  by  a  mixture  of  alcohol  and  ether. 

The  two  primary  albumoses  can  be  separated  by  treatment 
with  weak  32  per  cent,  alcohol.  The  filtrate  contains  the 
protalbumose  only. 

It  may  be  remarked  that  although  alcohol  will  precipitate 
the  primary  albumoses  it  does  not  coagulate  them.  They  can 
always  be  redissolved  and  in  this  respect  differ  from  the  true 
proteids.  They  are  not  denaturalized  even  by  long  standing 
under  alcohol  as  is  the  case  with  albumens. 

There  is  a  marked  difference  in  the  final  cleavage  products 
of  the  two  primary  albumoses. 

Heteroalbumose.  Protalbumose. 

Leucin,  little,  much. 

Tyrosin,  much,  trace. 

Glycocoll,  much,  none. 

Sulphur  loosely  combined,  some,  much  (1-2%). 

Neither  of  them  contains  a  carbohydrate  group. 


136  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTKY. 

B.  Secondary  Albumoses. 

Three  fractions  have  been  distinguished,  but  it  will  not  be 
profitable  to  enter  into  the  details  of  their  differences.  More 
of  the  true  proteid  reactions  are  missing  in  these  than  in  the 
primary  albumoses,  so  that  in  general  they  represent  a  further 
stage  of  cleavage  than  the  primary  albumoses  from  which  they 
can  be  obtained  by  hydrolysis. 

It  is,  however,  probable,  that  on  hydrolysis  of  proteid  some 
of  the  secondary  albumoses  are  split  off  direct  from  the  proteid 
molecule  without  passing  through  the  primary  stage.  One  in 
particular  called  synalbumose  contains  a  carbohydrate  group 
which  is  wanting  in  the  primary  albumoses,  so  cannot  have 
passed  through  those  stages. 

II.  Peptones. 

The  peptones  are  the  last  and  simplest  of  the  products  of 
hydrolysis,  which  still  retain  some  of  the  proteid  characteris- 
tics. They  are  readily  dialyzable  and  cannot  be  coagulated  by 
heat  or  precipitated  by  alcohol  or  saturated  ammonium  sul- 
phate. 

On  the  other  hand,  they  can  be  precipitated  by  the  alkaloid 
reagents,  showing  that  they  contain  diamino  acids,  and  they 
afford  the  biuret  test,  so  in  their  internal  construction  they  must 
still  be  closely  related  to  the  proteids.  They  are,  therefore, 
recognized  as  belonging  to  the  proteids,  using  the  term  in  its 
broadest  sense. 

Attempts  have  been  made  to  classify  the  peptones  according 
to  the  ease  or  difficulty  with  which  they  can  be  hydrolyzed  — 
Kuhne's  anti  and  amphopeptone  —  but  the  distinctions  drawn 
are  arbitrary  and  not  of  sufficient  value  to  discuss  in  detail. 

The  little  that  is  known  about  them  indicates  that  they  all 
closely  resemble  each  other. 


THE   PROTELDS.  137 


One  point  may  be  noted,  that  a  proteid  at  first  splits  into 
a  number  of  different  albumoses,  but  on  further  hydrolysis  the 
latter  split  into  peptones  between  which  only  slight  differences 
can  be  detected. 

Albumen 


Primary  albumose 
'\ 


Heteroalbumose          Protalbumose        Synalbumose 


Secondary  albumoses 


Peptones 
Amino  acids. 


III.  Binary  Compounds. 


Between  the  peptones  and  the  final  nuclei  there  are  probably 
some  intermediate  binary  compounds  temporarily  present,  but 
only  one  is  known,  Leucinimid,  composed  of  two  molecules 
of  leucin.  Arginin  and  cystin  are  binary  compounds,  but 
they  are  not  split  up  by  hydrolysis. 

No  doubt  from  the  commencement  of  hydrolysis  nuclei  are 
being  continually  split  off  as  such,  and  the  accompanying  table 
gives  a  hypothetical  summary  of  the  probable  course  of  events 
during  the  hydrolysis. 

The  actual  number  of  nuclei  in  each  intermediate  product  is 
not  known,  even  approximately,  but  there  are  reasons  for  be- 
lieving that  the  nuclei  in  the  original  proteid  molecule  may 
amount  to  100  or  120  in  some  cases. 


138 


OUTLINES    OF    PHYSIOLOGICAL    CHEMISTRY. 


Proteid  molecule 


First  Splitting. 


Synalbumoses. 
Up  to  25  nuclei. 


Peptone. 
Up  to  10  nuclei. 


Peptone. 
Up  to  10  nuclei. 


Third  Splitting. 

r+n  +  i+i+i+i+i+i 


Peptone. 
Up  to  10  nuclei. 


Binary. 
Compounds. 


Amino  acids. 

Nuclei. 


Fourth  Splitting. 


Binary. 
Compound. 


Amino  acids. 
Nuclei. 


up  to  120  nuclei. 


+  1+1+1+1+ 

Amino  acids. 
Nuclei  up  to  10. 

+    1+1+1+ 

Amino  acids. 
Nuclei  up  to  5. 

+  1+1+1+!+ 

Amino  acids. 
Nuclei  up  to  15. 


Amino  acids. 
Nuclei  up  to  5. 


Biuret 


We  may  compare  the  table  with  that  drawn  up  for  starch 
in  chapter  7,  the  processes  of  hydrolysis  in  each  case  being 
analogous. 

Polyamino  acids. 

I 


Amino  acids 


Dextrins    —    Monosaccharides. 


1 

I 

I 

Proteids 

Albumoses 

Peptones      — 

Polysaccharides 

I 
Starch 


—      Soluble  starch    — 


An  exact  comparison  cannot  very  well  be  made,  since,  in 
some  respects,  the  monosaccharides  are  more  comparable  with 


THE    PROTEIDS.  139 

the  peptones.  The  monosaccharides  are  still  carbohydrates  but 
the  ammo  acids  are  no  longer  proteid.  This  is  a  mere  matter 
of  nomenclature  but  the  peptones  and  monosaccharides  are  the 
forms  in  which  the  proteids  and  carbohydrates  respectively  are 
absorbed  and  utilized  by  the  body,  so  that  physiologically  they 
are  comparable. 

Still  the  amino  acids  and  monosaccharides  are  the  final 
products  of  hydrolysis  in  each  case,  whilst  the  peptones  and 
dextrins  are  intermediate  products.  By  regarding  the  proteids 
as  polyamino  acids  and  the  starches  as  polysaccharides  our 
method  of  comparison  seems  to  be  justified. 

ALBUMENOIDS. 

The  albumenoids  in  their  native  condition  are  insoluble  but 
some  of  them  can  be  hydrolyzed  to  soluble  forms.  The  final 
products  of  their  hydrolysis  are  the  same  as  those  of  true 
proteids.  Collagen  is  the  chemical  basis  of  white  fibrous  tissue, 
forming  as  such  the  frame  work  of  the  individual  organs  and 
tissues,  whilst,  mixed  with  lime  salts  to  form  the  bones,  it  con- 
stitutes the  framework  of  the  entire  body. 

It  is  resistant  to  gastric  digestion  but  can  be  hydrolyzed  by 
trypsin  or  boiling  with  dilute  acids. 

Gelatin  is  the  first  intermediate  product  of  its  hydrolysis  and 
this  stage  can  be  reached  by  prolonged  boiling  with  water  alone. 
Meat  on  cooking  becomes  more  tender  and  this  is  due  to  partial 
hydrolysis  of  collagen  to  gelatin.  Gelatin  itself  is  not  found 
in  the  living  tissues. 

Glue,  obtained  by  boiling  bones,  cartilage,  etc.,  is  simply 
impure  gelatin.  The  various  commercial  gelatins  are  more  or 
less  purified  glue. 

Gelatin  in  solution,  as  is  well  known,  dissolves  on  heating  and 
solidifies  (gelatinizes)  in  the  cold.  It  is  supposed  by  some  that  the 


140  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

power  of  gelatinization  depends  upon  the  presence  of  mineral  salts, 
but  the  purest  gelatin  obtainable,  containing  only  .04  per  cent,  of 
ash,  will  gelatinize  in  1  per  cent,  solution  so  that  the  role  of  the 
mineral  salts  does  not  appear  to  be  an  important  one. 

Gelatin,  although  tyrosin  cannot  be  obtained  from  it,  gives 
the  Millon  faintly  and  the  biuret  reaction  very  strongly  so  that 
it  is  of  a  proteid  nature,  but  there  appears  to  be  some  group  or 
groups  lacking  which  are  of  importance  for  nutrition  since  the 
nitrogen  contained  in  gelatin  cannot  entirely  take  the  place  of 
proteid  nitrogen. 

Gelatin,  therefore,  is  not  a  proteid  food  but  it  is  good  sparer 
of  nitrogen.  In  other  words  if  an  absolute  gelatin  diet  is  given 
there  is  less  waste  of  nitrogen  from  the  tissues  than  with  an 
absolute  carbohydrate  or  fat  diet. 

Elastin  is  the  basis  for  elastic  fibrous  tissue.  It  is  much 
more  resistant  than  collagen,  and  requires  prolonged  action  of 
hydrolytic  agents  before  it  is  broken  down.  Both  collagen  and 
elastin  on  hydrolysis  afford  albumoses  and  peptones  similar  to 
those  obtained  from  ordinary  albumen. 

Of  the  final  products  tyrosin  can  be  obtained  from  elastin 
though  not  from  collagen. 

Keratin. — The  function  of  keratin  is  different  from  that  of 
collagen.  It  is  not  a  supporting  medium  but  forms  the  external 
coverings  of  the  body,  horns,  hoofs,  hair,  etc.,  being  secreted  by 
the  epithelial  cells  of  the  epidermis  whilst  collagen  is  secreted 
by  the  connective  tissue  cells. 

Keratin  is  the  most  resistant  of  all  the  albumenoids  to  hydro- 
lytic agents,  and  can  only  be  decomposed  by  boiling  with  strong 
acids  or  alkalis. 

The  main  point  of  interest  is  its  high  sulphur  content,  4-5 
per  cent.  Cystin  is  present  in  large  quantities,  its  chief  source 
for  laboratory  experiments  or  other  uses  being  hoofs  or  hair. 


THE   PROTEIDS. 


141 


Albumenoids. 

Digestion  with 

Boiling  -with 

Pepsin. 

Trypsin. 

Water. 

Dilute  Acids. 

Strong  Acids. 

Collagen. 
Elastin. 
Keratin. 

0 
0 
0 

readily 
slowly 
0 

to  gelatin 
0 
0 

readily 
slowly 
0 

readily 
readily 
slowly 

This  merely  shows  the  relative  speed  of  hydrolysis. 

On  boiling  with  strong  acids  the  intermediate  proteoses  are 
quickly  decomposed,  and  the  nuclei  are  decomposed  to  some  ex- 
tent, so  the  products  cannot  be  compared  with  those  derived  from 
digestion  with  trypsin  or  dilute  acids.  Cystin,  however,  is  not 
affected  and  can  be  obtained  as  such  from  keratin. 

PROTEIDES. 

There  are  certain  proteids  which  by  mild  action  of  a  hydro- 
lytic  agent  may  be  split  into  two  parts,  one  of  which  is  always 
a  complete  proteid  body,  the  other  being  organic  but  not  a 
proteid.  This  is  analogous  to  the  cleavage  of  the  glucosides  into 
two  atom  groups  one  of  which  is  always  a  sugar.  Hoppe- 
Seyler  in  consideration  of  the  analogy  with  the  glucosides  has 
designated  the  complex  albuminous  bodies  the  proteides.  By 
English  authors  they  are  generally  called  compound  proteids. 
Three  classes  of  these  compound  proteids  may  be  considered, 
glyco-proteids,  hemoglobins  and  nucleo-proteids. 

Albumen 
1.   Glycoproteids,  MueinsS 

Glycosamin 

On  cleavage  with  acids  these  bodies  very  readily  yield  a  re- 
ducing substance,  glycosamin,  and  proteid.  They  are  viscous 
colloid  substances  of  a  marked  acid  nature,  dissolving  readily 
in  dilute  alkalies  from  which  solution  they  are  precipitated  by 
acetic  acid.  The  precipitation  by  acetic  acid  is  used  to  obtain 
the  mucin  from  mixed  solutions. 


142  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

They  are  not  coagulated  by  heat  but  are  denaturalized  by 
long-continued  action  of  acids,  alkalies  or  alcohol.  Their  ele- 
mentary analysis  shows  considerable  difference  from  the  true 
proteid,  the  difference  being  due  to  the  large  amount  of  glyco- 
samin,  which  contains  less  N  and  more  O  than  true  proteid. 

c.         H.          N.  s.         o. 

Mucin  48          6.5          11.5          .8          32  per  cent. 

Proteid  52          7  16  .5          22  per  cent. 

Certain  mucins  have  been  found  to  yield  as  much  as  30  per 
cent,  of  a  reducing  substance.  The  nature  of  the  proteid  part 
of  the  molecule  has  been  neglected  for  a  study  of  the  reducing 
substance. 

MUCOIDS. 

These  compounds  have  a  great  similarity  to  the  mucins  from 
which  they  are  distinguished,  not  sharply,  by  certain  physical 
properties.  They  are  less  slimy  than  mucins,  but  the  difference 
between  mucins  and  mucoids  are  only  of  degree  not  of  kind. 

The  name  mucin  is  now  restricted  to  the  slimy  substances 
secreted  by  epithelium ;  all  other  compounds  having  a  similar 
behavior  being  called  mucoids. 

Mucoids  have  been  obtained  from  tendon,  umbilical  cord, 
white  of  eggs,  blood  serum,  ascitic  fluid  and  cartilage.  They 
are  all  easily  hydrolyzed  with  the  direct  release  of  glycosamin 
except  in  one  instance,  chondromucoid  from  cartilage,  which 
has  certain  characteristic  cleavage  products  distinguishing  it 
from  all  other  mucoids. 

When  chondromucin  is  boiled  with  dilute  acids  there  appears, 
in  addition  to  the  usual  cleavage  products  of  proteid,  a  sulphur 
containing  chondroitin. 

By  further  cleavage  with  dilute  hydrochloric  acid  all  the  sul- 
phur is  split  off  as  sulphuric  acid,  showing  that  the  original 
compound  was  in  the  form  of  chondroitin  sulphuric  acid. 
Chondroitin  has  no  reducing  action,  but  on  further  cleavage 


THE   PEOTEIDS. 


143 


affords  a  reducing  body,  chondrosin,  and  diacetic  acid,  the  latter 
being  at  once  split  up  into  two  molecules  of  acetic  acid. 

Chondrosin  on  cleavage  with  alkali  yields  glycosamin  and 
glycuronic  acid.  ^^  mucoid 

(Acid  hydrolysis) 


Proteid 
Usual  products 


Chondroitin 
sulphuric  ester 


Chondroitin      Sulphuric  acid 


Chondrosin  Diacetic  acid 

(Alkali  hydrolysis) 

/  \  Acetic    Acetic 

/  \  acid        acid 

Glycosamin  Glycuronic 

acid 


>.—  CO-CH2— CO— CH3 
^H-N=CH—  (CHOH^— COOH 
tfHOH), 

,— O— SO3H 

Chondroitin  sulphuric  ester 


m— CO— CH8— CO-CH, 
CH— N=CH— (CHOH^— COOH 
(OHOH), 
CH2OH 

Chondroitin  +  sulphuric  acid. 


to 


H— N=CH— (CHOH)4-COOH 
(CHOH), 


Chondrosin 


Diacetic  acid  (acetacetic  acid). 


CHO 


bCH2OH 
jlycosamin 


(9HOH), 
COOH 

Glycuronic  acid. 


144  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

Chondroitin  sulphuric  acid  therefore  is  glycosamin  with 
various  atom  groups  attached  which  can  be  split  off  one  by  one. 
Phosphoglycoproteids.  —  The  mucins  and  mucoids  already 
considered  do  not  contain  phosphorus  and  in  this  respect  differ 
from  the  phospho-glycoproteids.  The  latter  on  gastric  diges- 
tion yield  a  reducing  carbohydrate  and  a  phosphorized  proteid 
group.  They  are  of  little  importance,  being  only  found  in 
invertebrate  animals. 

Globin 
II.  Hemoglobin^ 

Hematin 

Hemoglobin  (Hb)  is  the  red  coloring  matter  found  in  the 
blood  of  all  vertebrates.  It  consists  of  a  proteid,  globin,  com- 
bined with  a  non-proteid  iron-containing  pigment. 

Globin  is  a  member  of  a  peculiar  group  of  .proteids  called 
histons  which  will  be  described  later. 

The  precipitation  and  color  reactions  of  hemoglobin  are 
those  common  to  proteids,  but  it  differs  in  two  respects  from 
all  other  proteids. 

1.  It  crystallizes  easily. 

2.  It  has  the  property  of  forming  loose   compounds  with 
oxygen,  carbon  monoxide,  nitric  oxide  and  some  other  gases. 

It  is  present  in  the  red  blood  corpuscles  as  a  loose  compound 
with  some  other  constituent  of  the  cell.  The  chief  method  of 
distinguishing  the  varieties  of  Hb  and  its  derivatives  is  by 
means  of  the  spectroscope.  Since  space  does  not  permit  us  to 
deal  with  spectrum  analysis,  we  can  only  touch  lightly  on  the 
hemoglobins. 

It  is  necessary  to  distinguish  between  oxyhemoglobin  (HbO) 
and  reduced  hemoglobin  (Hb).  The  blood  in  the  lungs  is 
saturated  with  oxygen,  HbO  is  formed  and  in  the  course  of  the 
circulation  oxygen  is  given  up  again  to  the  tissues,  leaving  the 


THE    PKOTEIDS.  145 

Hb  in  the  reduced  condition.  The  reduced  Hb  solution  is 
very  dark  colored  (venous  blood),  whilst  HbO  is  bright  red 
(arterial  blood). 

The  amount  of  oxygen  which  combines  with  the  Hb  is  not 
constant  but  varies  with  the  pressure  of  the  oxygen  gas.  In 
this  respect  it  behaves  much  as  gases  in  aqueous  solution.  By 
exhausting  blood  under  the  bell  jar  of  an  air  pump  all  the 
oxygen  may  be  removed. 

HbO  crystallizes  more  easily  than  Hb,  and  is  therefore  more 
readily  obtained  in  pure  form.  Being  thus  by  far  the  most 
easily  crystallizable  of  all  proteids  it  has  been  the  favorite  one 
used  in  molecular  weight  determinations.  The  empirical  for- 
mula has  been  approximately  determined  as  C758H1203N195O218FeS3 
for  dog's  hemoglobin. 

METHEMOGLOBIN. 

In  addition  to  the  labile  oxyhemoglobin,  there  is  another 
oxygen  compound  of  hemoglobin.  This,  methemoglobin,  is 
stable  in  that  it  will  not  give  up  its  oxygen  in  a  vacuum.  A 
great  many  substances  have  the  power  of  inducing  the  forma- 
tion of  this  compound,  and  it  is  often  formed  in  the  blood  ves- 
sels by  the  action  of  poisons.  In  this  condition  the  oxygen 
cannot  be  utilized  by  the  body  cells. 

CARBON  MONOXIDE  HEMOGLOBIN,  HbCO 
Is  formed  when  carbon  monoxide  comes  in  contact  with  hem- 
oglobin. It  is  a  comparatively  stable  substance ;  the  gas 
is  given  off  in  a  vacuum  very  slowly.  If  the  carbon  monoxide 
is  present  in  the  air  it  combines  with  the  hemoglobin  to  the 
exclusion  of  the  oxygen  because  it  has  a  greater  affinity  for  and 
forms  a  more  stable  compound  with  it.  The  tissues  die  for 
lack  of  oxygen.  The  great  danger  in  gas  poisoning  at  the 
10 


146  OUTLINES   OF    PHYSIOLOGICAL   CHEMISTKY. 

present  day  is  due  to  the  fact  that  a  large  percentage  of  the  gas 
furnished  is  carbon  monoxide. 

Hemoglobin  forms  compounds  with  many  other  gases,  but 
they  are  not  of  sufficient  importance  to  describe  here. 

HEMATIN. 

Hematin  is  the  non-proteid  iron-containing  pigment  obtained 
by  cleavage  of  hemoglobin,  a  change  which  takes  place  very 
quickly  in  acid  solution.  If  oxygen  is  excluded  during  the 
cleavage  hemochromogen  and  not  hematin  results.  Hemo- 
chromogen  may  be  considered  as  reduced  hematin,  the  former 
being  a  ferro  compound  while  the  latter  isferri.  The  oxidation 
and  reduction  of  this  substance  is  accomplished  almost  as  read- 
ily as  with  hemoglobin,  and  there  are  reasons  for  believing  that 
the  latter  is  an  ester  of  the  acid  hematin  with  the  basic  globin. 

Hematin  itself  does  not  crystallize,  but  chlorhematin  obtained 
by  the  action  of  HC1,  by  which  Cl  is  substituted  for  an  OH 
group,  crystallizes  readily  and  has  been  the  subject  of  much 

study. 

C32H32N4Fe04  +  HC1  m+~  C32H31ClN4FeO3  +  H2O 


Hematin.  Hemin  or  chlorhematin. 

The  hemin  crystals  obtained  from  different  animal  species  are 
to  some  extent  characteristic. 

Hematin  on  cleavage  with  acids,  e.  g.  HBr,  yields  hemato- 
porphyrin,  a  pigment  containing  no  iron,  which  has  been  shown 
to  be  isomeric  with  one  of  the  bile  pigments,  bilirubin.  Hema- 
toporphyrin  is  much  darker  than  hematin.  The  bright  red  color 
of  the  latter  is  due  to  the  Fe. 


2H2O  +  2HBr  =  2C16H18N203-f  FeBr2  +  Ha 

Hematin.  Hematoporphyrin. 

It  is  of  interest  to  note  that  chlorophyll,  the  iron-containing 
respiratory  pigments  of  plants,  yields  a  similar  compound,  phyl- 


THE   PROTEIDS.  147 

loporphyrin,  on  cleavage  with  acids.     The  other  bile  pigments 
are  derived  from  bilirubin  by  oxidation  and  reduction  processes. 

III.   NUCLEO-PROTEIDS. 

Nucleo-proteids  are  the  chief  constituent  of  cell  nuclei  and 
are  therefore  most  abundant  in  glandular  organs.  They  are 
compounds  of  proteid  with  nucleic  acid,  and  the  generally  ac- 
cepted view  of  their  decomposition  is  as  follows. 

Nucleo-proteid 


Nuclein      Proteid 

r       \ 

Nucleic          Proteid 
acid 

/n 

Pyrimidin    Purin    Phosphoric 
Bases.       Bases.         acid. 

All  uucleo  proteids  do  not  pass  through  the  exact  number  of 
steps  given  above,  and  this  scheme  applies  only  in  a  general 
way.  The  proteid  part  of  the  molecule,  as  well  as  the  nucleic 
acid,  shows  great  variation.  But  a  characteristic  of  these  com- 
pounds is  the  high  percentage  of  phosphorus. 

C.         H.         N.         P.  S.         O. 

48.5          7          17       1.5^          .7         24. 

When  subjected  to  gastric  (pepsin  +  .2  per  cent.  HC1)  diges- 
tion, proteid  is  split  off  and  hydrolyzed  to  soluble  albumoses 
and  peptones,  but  the  residue,  (nuclein),  containing  all  the  phos- 
phorus, remains  undissolved. 

Nuclein,  therefore,  is  much  richer  in  P  than  the  original 
nncleo -proteid,  containing  3-5  per  cent. 

Gastric  juice  has  little  effect  upon  nuclein,  but  in  the  in- 
testine the  digestion  is  completed. 


148  OUTLINES    OF   PHYSIOLOGICAL   CHEMISTRY. 

All  the  P  of  the  original  molecule  is  found  in  the  nucleic 
acids  of  which  the  elementary  percentages  are  : 

C  37ft   H  4ft   N  15ft   O  34ft    P  10ft 

Nucleic  acid  can  be  dissolved  in  strong  acids,  and  if  to  such 
a  solution  albumose  is  added,  precipitates  are  formed  which 
show  a  remarkable  similarity  to  nucleo-proteids,  indicating  that 
proteid,  or  its  modifications,  has  a  strong  affinity  for  nucleic 
acid. 

On  further  digestion  with  trypsin  or  on  boiling  with  strong 
(5  per  cent.  HC1)  acid,  nucleic  acid  is  broken  up  into  its  final 
products,  phosphoric  acid  and  the  soluble  purin  bases. 

The  nucleo-proteids  differ  to  some  extent  according  to  the 
different  organs  from  which  they  are  obtained  and  some  of  them 
yield  pyrimidin  bases  also,  —  thymin,  uracil,  —  but  these  are 
of  much  less  importance  than  the  purin  bases  and  need  not  be 
considered.  The  different  nucleic  acids  yield  varying  propor- 
tions of  the  following : 

Adenin  C5H5N5 

Guanin  C6H6N6O      also  called  Xanthin  bases  or 

Hypoxanthin     C5H4N4O          Alloxuric  bases. 

Xanthin  C5H4lSr4O2 

The  simplest  method  of  obtaining  the  purin  bases  from  the 
products  of  proteolysis  is  by  precipitating  them  with  silver 
nitrate,  AgNO3,  from  the  solution  made  strongly  alkaline  with 
ammonia. 

AgNO3  +  NH3  +  H  -  purin     base  =  NH4NO3  +  Ag  - 
purin  base. 

The  silver  compound  thus  formed  is  decomposed  by  H2S, 
forming  insoluble  AgS,  and  setting  the  bases  free. 

Uric  acid,  C5H4N4O3,  trioxypurin,  is  an  oxidation  product 
of  these  bases  and  it  has  been  found  that  in  the  course  of 


THE   PROTEIDS.  149 

metabolism  in  the  human  body  a  portion  of  the  nuclein  waste 
is  excreted  as  uric  acid. 

Such  a  decomposition  as  that  figured  above  for  nucleo-proteids, 
resulting  in  purin  bases,  takes  place  in  the  body  tissues,  and  it 
has  been  proved  that  certain  organs,  liver  and  thymus,  can 
oxidize  a  portion  of  these  to  uric  acid.  The  method  of  demon- 
strating this  is  of  interest.  The  liver  is  taken  from  the  animal 
at  the  moment  of  death,  ground  to  pulp  as  quickly  as  possible, 
nuclein  or  purin  bases  added,  and  the  whole  kept  at  40°  C. 
In  three  or  four  hours  uric  acid  is  found  to  be  present.  It 
seems  probable  that  all  tissues  take  part  in  such  a  formation  of 
uric  acid  in  proportion  to  their  content  of  nuclein.  The  nuclein 
bases  taken  in  the  food  suffer  the  same  fate  as  those  originating 
from  destruction  of  body  tissue  and  accordingly  the  total  uric 
acid  excreted  may  be  divided  into  two  protocols. 

The  Endogenous,  that  part  which  comes  from  the  purin  bases 
of  body  tissue. 

The  Exogenous,  that  portion  which  comes  from  the  purin  bases 
of  the  food. 

In  digestion  the  nucleo-proteids  are  split  up  by  pepsin  in  the 
stomach  to  proteid  +  nuclein.  The  nuclein  is  then  decomposed 
by  trypsin  to  nucleic  acid  -f-  proteid  in  the  small  intestine,  and 
the  nucleic  acid  to  the  purin  bases  which  are  absorbed  as  such  ; 
little  or  none  passing  out  with  the  feces. 

With  an  ordinary  meat  diet  the  purin  bases  absorbed  are  in 
excess  of  the  needs  of  the  organism,  the  excess  representing  the 
exogenous  portion  of  the  uric  acid. 

When  the  diet  is  regulated  so  that  no  purin  bases  are  taken 
in  with  the  food  the  uric  acid  output  is  materially  lessened. 

Much  of  the  experimental  work  on  the  production  and  destruc- 
tion of  uric  acid  in  the  animal  body  has  been  confusing  because 
different  species  of  animals  used  by  different  investigators  rueta- 


150  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

bolize  proteid  in  dissimilar  ways.  Obviously  it  is  impossible  to 
gain  exact  knowledge  of  uric  acid  metabolism  in  man  by  a  study 
of  birds  because  the  latter  excrete  practically  all  of  their  waste 
nitrogen  as  uric  acid,  which  calls  for  a  synthetic  formation  of 
the  same  whilst  in  man  and  other  mammals  such  a  process  is 
probably  of  little  importance. 

It  has  been  stated  above  that  uric  acid  may  be  formed  in  the 
liver  by  simple  oxidation  of  xanthin  or  hypoxanthin  but  this 
statement  tells  only  half  the  truth,  for  the  process  continues  and 
results  in  a  destruction  of  a  portion,  at  least,  of  the  uric  acid 
thus  formed.  There  are  thus  two  processes  taking  place 
simultaneously  in  this  organ  and  in  one  animal  species  the 
formation,  whilst  in  another  the  destruction  of  uric  acid  is  the 
predominant  action. 

For  instance,  if  a  dog's  liver  is  removed  immediately  after  the 
death  of  the  animal,  tubes  inserted  in  the  hepatic  artery  and 
vein  so  that  defibrinated  blood  may  be  passed  through  and  the 
whole  kept  at  a  temperature  of  38°  C.  the  organ  is  surviving  and 
shows  its  normal  activities.  By  carefully  oxygenating  the  blood 
supply  the  organ  may  be  kept  alive  for  some  hours.  Such 
perfusion  experiments  have  proved  that  uric  acid  added  to  the 
arterial  blood  is  oxidized  (to  urea)  by  the  liver  cells.  The  cells 
of  other  tissues,  muscles,  kidneys,  etc.,  do  the  same,  so  that  not 
all  the  uric  acid  formed  in  the  course  of  metabolism  is  excreted 
as  such  and  in  a  general  way  we  may  say  that  the  uric  acid 
excreted  represents  the  portion  which  has  escaped  oxidation  in 
the  body. 

Besides  the  breaking  down  there  is  constant  building  up  by 
cells  to  repair  waste.  Cell  metabolism  maintains  the  necessary 
equilibrium. 

We  may  therefore  trace  three  sources  for  urea,  two  of  which 
have  been  dealt  with  previously. 


THE   PROTEIDS. 


151 


1.  Glvcocoll,  obtained  by  oxidation  of  the  ordinary  proteid 
nuclei. 

2.  Guanidin  hydrolyzed  from  its  combination  with  ornithin. 

3.  Uric  acid  derived  from  nucleic  acid. 

We  may  again  point  out  that  uric  acid  is  not  always  a  pre- 
cursor of  urea  as  was  formerly  supposed. 


Nucleo  Proteids 


In  tissues 
(Cell  metabolism) 


In  food 
(Gastric  digestion) 


Nuclein  Proteid 

(Tryptic  digestion) 


Proteid  Nuclein 

./\ 


Proteid    Nucleic  acid  / 

Nucleic  acid  Proteid 

(Tryptic  digestion) 


Phosphoric  acid  Purin  bases  Purin  bases    Phosphoric  acid 

(Oxidized  by        (Absorbed  and 
liver,  &c. )     oxidized  by  liver,  &c. ) 


f  Uric  acid 

Endogenous         (Partly  oxidized  by  liver,  &c.)         Exogenous. 


Urea,  CO2,  H2O 
(Excreted). 


Uric  acid 
(Excreted). 


152         OUTLINES  OF  PHYSIOLOGICAL  CHEMISTRY. 

OTHER  PROTEIDS. 

We  have  so  far  considered  typical  proteids,  the  albumens, 
and  their  modifications,  but  there  are  some  proteids  adapted  for 
special  purposes,  which  have  not  the  character  of  albumens. 
They  appear  to  be  closely  related  to  the  albumens  but  are  not 
modifications  of  them  in  the  sense  in  which  proteoses  and 
albumenoids  are  regarded  as  modifications,  so  will  be  discussed 
as  separate  groups.  One  can  think  of  them  as  specialized 
albumens. 

I.  Phosphorized  Proteid. 

Casein,  the  principal  milk  proteid,  is  the  most  important  rep- 
resentative of  this  group. 

Casein  does  not  coagulate  on  boiling  but  its  nutritive  proper- 
ties are  impaired,  and  it  is  found  that  some  sulphur  is  split  off, 
so  it  must  undergo  some  chemical  changes.  In  addition, 

1.  It  contains  no  carbohydrate  group. 

2.  It  contains  phosphorus. 

1.  Is  of  physiological  interest.     Free  sugar  exists  in  milk 
in  the  form  of  lactose,  and  it  is  from  this  that  the  sucking 
mammal  derives  its  carbohydrates,  so  there  is  no  necessity  for 
these  being  present  in  the  proteid  source  of  nourishment. 

On  the  other  hand  eggs  contain  no  free  sugar  and  the  embryo 
bird  can  only  derive  its  carbohydrates  from  the  carbohydrate 
group  combined  in  the  egg  albumen. 

2.  Since  casein  contains  phosphorus  it  resembles  the  nucleo- 
proteids  in  this  respect  and  is  often  called  a  pseudo-nuclein  or 
nucleo-albumen.     But  nucleic  acid  is  absent,  so  these  terms  are 
misleading  and  it  is  better  to  regard  casein  simply  as  a  phos- 
phorized  proteid.     As  with  the  nucleo-proteids  the  P  is  present 
as  phosphoric  acid  in  combination,  but  it  is  here  in  direct  com- 
bination with  the  proteid,  whilst  in  the  nucleo-proteids  the  P 


THE   PROTEIDS.  153 

is  a  constituent  of  the  nucleic  acid,  not  being  found  in  the  split- 
off  proteid. 

Casein.  Nucleo-proteid. 

Proteid — phosphoric  acid.  Proteid — nucleic  acid. 


Purin     Phosphoric 
bases.          acid. 

Phosphorus  is  necessary  for  the  suckling  and  is  obviously 
supplied  by  means  of  the  casein.  In  the  egg  nucleo-proteids 
are  present  in  the  yolk,  and  afford  the  phosphorus  required  by 
the  embryo  bird. 

Whilst  on  the  subject  of  phosphorus  a  slight  digression 
may  be  made.  Phosphorus  is  required  not  only  for  building 
up  the  nucleo-proteids  of  the  nuclei,  but  also  for  nervous  tissue 
which  contains  a  large  amount  of  P  in  the  form  of  lecithin,  a 
phosphorized  fat  occurring  in  combination  with  proteid. 

II.  Basic  Proteids. 
Histons  and  protamins. 
These  differ  from  albumens  : 

1.  In  not  being  coagulableby  heat. 

2.  In  being  distinctly  basic.     They  have  no  acid  qualities, 
so  do  not  give  the  amphoteric  reaction  of  the  albumens.     This 
basic  character  is  due  to  the  relatively  large  quantities  of  the 
hexon  bases  they  contain. 

They  afford  most  of  the  color  reactions,  but  contain  no  car- 
bohydrate group.  The  biuret  reaction  is  very  marked  and 
this  is  probably  due  to  the  comparatively  large  number  of  free 
NH2  groups. 

(a)  The  histons  on  account  of  their  distinctly  basic  qualities 
combine  more  readily  with  acids  than  the  ordinary  albumens, 
and  are  therefore  specially  adapted  for  the  combinations  occur- 
ring in  some  of  the  proteides. 


154  OUTLINES    OF   PHYSIOLOGICAL   CHEMISTRY. 

1.  Hemoglobin  is  a  liiston   in  combination   with  the  acid 
hematin. 

2.  Some  of  the  nucleo-proteids  are  histon  in  combination  with 
nucleic  acid. 

These  are  the  two  forms  in  which  histon  occurs  in  animal 
tissue,  and  in  studying  histon  the  acids  must  first  be  split  off 
in  either  case.  But  any  method  which  can  be  employed  for 
this  purpose  must  at  the  same  time  bring  about  a  partial  hydrol- 
ysis of  the  proteid,  so  that  the  histons  as  obtained  for  study 
cannot  be  regarded  as  the  exact  representatives  of  the  original 
proteid  part  of  the  molecule. 

For  instance,  histons  are  not  coagulated  by  heat  but 
hemoglobin  and  the  histon  containing  nucleo-proteids  are 
coagulated.  In  these  cases  it  cannot  be  the  hematin  and 
nucleic  acid  respectively  which  are  responsible  for  the  coagu- 
lation. 

The  only  way  of  distinguishing  the  proteid  part  (histon)  of 
these  substances  from  true  albumens  is  by  noting  its  distinctly 
basic  qualities,  and  observing  that  on  hydrolysis  it  yields  the 
hexon  bases  in  larger  quantities  than  usual.  There  is  no 
reason  for  supposing  that  the  average  histon  molecule  is  smaller 
than  that  of  the  albumens,  although  they  are  often  assumed  to 
be  simpler  substances.  This  is  no  doubt  true  of  the  form  in 
which  they  are  studied,  but  probably  not  of  that  in  which  they 
exist  in  the  entire  molecule. 

In  speaking  of  the  proteid  of  hemoglobin  and  of  the  nucleo- 
proteids  as  albumens  in  the  earlier  part  of  this  chapter  this 
was  done  for  the  sake  of  simplicity  and  in  order  to  avoid  con- 
fusion. It  is  now  evident  however  that  albumen  and  histon , 
are  so  closely  allied  that  it  is  difficult  to  say  there  is  any  real 
difference  between  them.  Histon  probably  does  not  vary  from 
true  albumens  more  than  albumens  may  vary  among  them- 


THE   PROTEIDS.  155 

selves.  It  only  varies  in  a  direction  which  makes  a  distinction 
easier,  i.  e.,  in  being  decidedly  basic. 

(5)  Protamins  vary  more  from  the  albumens  than  the  histons, 
being  even  more  strongly  basic,  and  possessing  a  simpler 
structure.  Most  of  our  knowledge  concerning  them  we  owe  to 
Kossel,  who  considers  them  as  representing  the  central  portion, 
or  proteid  nucleus,  around  which  the  more  complicated  albu- 
mens are  built  up.  But  there  is  no  conclusive  evidence  to  show 
that  this  is  the  case.  They  are  never  found  as  intermediate 
products  of  hydrolysis,  but  exist  preformed  in  fresh  tissues  from 
which  they  can  be  obtained  direct. 

The  protamins  are  not  widely  distributed,  their  principal 
source  being  the  spermatozoa  of  fish. 

It  is  likely  that  they  are  specially  adapted  for  fertilizing 
processes,  but  this  has  not  been  demonstrated. 

The  chief  feature  of  the  protamins  is  the  large  amount  of 
arginin  they  contain,  sometimes  over  80  per  cent.,  e.  g.,  sper- 
matozoa of  salmon  (salmin).  Since  the  protamins  are  nondia- 
lyzable  the  molecule  must  be  large,  and  it  is  quite  possible  that 
their  molecular  weight  is  not  much  below  that  of  albumen,  but 
being  built  up  of  fewer  kinds  of  nuclei,  their  structure  may  be 
considered  simpler  in  this  respect. 

Applying  the  symbol  used  for  the  proteid  molecule,  we  may 
suppose  that  of  each  ten  nuclei  in  salmin  protein,  eight  are  ar- 
ginin. 

Arginin.  Arginin.  Leucin.  Arginin.  Arginin. 

We  may  suppose  the  linkage  to  occur  as  usual  by  means  of 
the  alpha-ammo  acid  groups,  so  that  for  each  additional  mole- 
cule of  arginin  there  would  be  an  increase  in  basic  qualities  due 
to  the  free  guanidin  end  of  the  chain.  The  protamin  may  be 
considered  as  polyarginin  to  the  extent  of  80  per  cent.,  whilst 


156 


OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 


the  average  albumen  is  polyleucin  to  the  extent  of  40  per  cent, 
or  50  per  cent. 

To  separate  protamins  from  other  proteids  the  solution  is 
boiled.  This  disposes  of  the  coagulable  proteids,  and  the  pro- 
tamins can  be  separated  from  other  non-coagulable  proteid  by 
NH3.  They  exist  as  soluble  salts  in  combination  with  an  acid, 
and  the  NH3  drives  them  from  combination,  forming  NH4  salts. 
The  protamins  thus  liberated  are  insoluble  and  precipitate  out. 

Unlike  the  histons,  the  protamins  can  be  obtained  in  their 
native  condition.  No  hydrolytic  action  is  necessary  to  drive 
them  from  a  special  combination. 

The  protamins  on  hydrolysis  yield  intermediate  products 
called  protons.  These  appear  to  be  somewhat  different  from 
the  proteoses,  but  the  differences  are  probably  simply  due  to 
the  relatively  large  quantities  of  arginin. 

A  table  of  hexon  bases  found  in  various  proteids  may  be 
given  for  comparison. 


Arginin. 

Lysin. 

Histidin. 

Salmin.     Protamin  from  salmon  sperm. 
Sturin.     Protamin  from  sturgeon  sperm. 
Histon  from  thymus. 
Gelatin. 
Casein. 
Egg  albumen. 

84 
58 
14.5 
9 
4.5 
0.8 

0 

12 
7.5 
5 

2 
trace 

0 
12 
1.2 
trace 
2.5 
0 

III.  Melanins.     Pigments. 

The  group  tryptophan  or  proteinochromogen  which  has 
recently  been  identified  as  skatolamino-acetic  acid,  has  long 
been  considered  to  be  the  precursor  of  animal  pigments. 

Melanoidin  is  the  term  applied  to  pigments  obtained  on 
artificial  hydrolysis  with  acids  whilst  melanin  applies  to  the 
natural  pigments  of  the  skin,  hair  and  retina.  They  are  both 
very  resistant  bodies  and  in  origin  probably  have  no  relation  to 


THE    PROTEIDS.  157 

the  blood  coloring  substance  hematin.  The  high  sulphur  con- 
tent of  many  of  them  does  not  accord  with  such  an  origin,  nor 
do  the  greater  part  of  them  contain  any  iron. 

Mdanoidins.  —  The  structure  of  those  coloring  substances 
which  are  obtained  by  boiling  proteids  with  mineral  acids  is 
very  complex  and  most  of  the  work  done  thus  far  has  been  in 
the  line  of  ultimate  analysis.  Such  work  has  not  been  without 
some  results,  for  it  has  established  that  these  "  melanoidins  "  as 
they  are  called  have  wide  variations  in  composition.  But  the 
one  important  fact  in  regard  to  structure  is  that  on  fusion  with 
caustic  potash  they  yield  indol  and  skatol  which  harmonizes 
with  the  tryptophan  idea  of  origin. 

Melanins.  —  The  difficulty  of  getting  the  melanins  in  pure 
form  has  hindered  a  study  of  their  structure  but  so  far  as  this 
has  been  possible,  elementary  analysis  shows  marked  differences 
in  composition.  Fusion  with  potash  yields  indol  and  skatol 
bodies  as  with  the  melanoidins,  but  until  more  complete  studies 
are  made  of  their  decomposition  products  it  is  of  little  use  to 
say  more  about  them. 

On  fusion  with  potash  indol  and  skatol  may  be  formed  by 
condensation  of  tyrosin  as  well  as  from  tryptophan  and  some 
pigments  appear  to  be  directly  derived  from  tyrosin  by  a  proc- 
ess of  oxidation.  The  liquid  resembling  ink  found  in  the 
squids  has  been  shown  to  be  such  an  oxidation  product  of 
tyrosin. 

Since  the  melanins  are  absolutely  resistant  to  hydrolysis,  it 
is  impossible,  as  with  albumens  or  protamins,  to  find  out  of 
what  nuclei  they  are  composed.  About  all  we  know  is  that 
fusion  of  a  very  minute  amount  with  KOH  gives  rise  to  very 
bad  smells,  of  skatol  and  indol,  so  that  in  all  probability  the 
tryptophan  or  tyrosin  rings  or  both  are  very  largely  repre- 
sented. Taking  them  at  about  70  per  cent.,  and  using  our 


158  OUTLINES    OF   PHYSIOLOGICAL   CHEMISTRY. 

symbol  for  the  last  time  we  may  suppose  the  melanins  to  be 
constructed  somewhat  as  follows  : 


Tryptophan.        Tyrosin.  Leucin.  Tyrosin.      Tryptophan.    Glutamic  acid. 

With  the  ink  of  squids  and  some  vegetable  pigments  the  entire 
molecule  appears  to  be  constructed  of  tyrosin  or  some  oxidized 
form  of  tyrosin  so  that  these  may  be  considered  as  polytyrosins. 

Our  contention  that  these  groups  of  proteids  just  discussed 
are  specialized  albumens  seems  to  be  justified. 

1.  Casein  is  especially  adapted   for  sucklings  in  containing 
phosphorus  and  in  being  easily  digested.     Since  no  carbohy- 
drate group  is  required,  this  is  dispensed  with. 

2.  Basic  Group. 

(a)  Histons.  —  Specially  adapted  for  combination  with  cer- 
tain acid  radicals  which  are  required  for  definite  purposes. 
(5)  ProtammSj  probably  specially  adapted  for  fertilization. 

3.  Melanins.  —  Resistant  bodies  specially  adapted  for  absorp- 
tion of  heat  and  light  rays.     This  property  of  the  melanins 
cannot  be  discussed  here,  since  it  entails  the  question  of  spec- 
trum analysis. 

We  have  said  there  are  reasons  for  supposing  that  the  proteid 
molecule  may  be  composed  of  100  to  120  nuclei.  To  close  the 
chapter  we  may  explain  those  reasons  briefly. 

The  molecular  weight  of  proteid  is  difficult  to  estimate  for 
various  reasons,  not  the  least  important  being  the  difficulty  of 
getting  a  proteid  in  pure  condition. 

This  however  does  not  apply  so  forcibly  to  hemoglobin  which 
is  easily  crystallizable.  Its  molecular  weight  has  been  esti- 
mated in  various  ways. 

1.  By  0  absorption,  100  grams  Hb  absorbs  .2246  grams  O2. 
.2246  :  100  : :  32  :  1^250  molecular  weight. 


THE    PROTEIDS.  159 

2.  Sulphur  content  is  .43  per  cent. 

With  lead  acetate  only  part  of  the  S  is  parted  with,  so  there 
must  at  any  rate  be  two  atoms  of  S  in  the  molecule.  S2  =  64. 

.43  :  100  ::  64  :  14,883  molecular  weight. 

/Hematin  4.2  per  cent,  molecular  weight  is  592. 

3.  Hb 

\Globin. 

4.2  :  100  ::  592  :  14,100  molecular  weight. 

4.  Estimation  from  Fe  content  works  out  at  about  16,000. 
These  estimations  agree  fairly  closely,  so  we  may  take  the 

average  at  15,000.  Deducting  600  for  hematin  leaves  14,400 
for  the  molecular  weight  of  the  globin. 

The  average  molecular  weight  of  the  nuclei  is  about  140,  and 
each  time  a  nucleus  enters  into  combination  there  is  loss  of 
H2O,  having  a  molecular  weight  of  18.  We  may  then  take  the 
average  nucleus  in  combination  as  120  molecular  weight. 

14,400  -r-  120  =  120 ;  about  the  probable  number  of  nuclei 
in  the  proteid  molecule  in  this  instance  at  any  rate. 

TABLE  OF  PKOTEIDS. 

1.  Albumen, 

2.  Albumen  modified  by  digestion. 

xAlbumoses 
Proteoses^ 

^Peptones 

3.  Albumen  modified  by  body  cells. 

/Collagen 

Albumenoids^-  Elastin 
\Keratin 

4.  Albumen  plus  something  else. 

a.  Albumen  +  glycosamin  =  Glycoproteids. 

b.  u  (histon)  -f-  hematin  =  Hemoglobin. 

c.  "      (sometimes  histon)  -f  nucleic  acid  =  Nucleo-proteids. 

5.  Albumen  specialized. 

a.  Albumen  phosphorized,  Casein. 

b.  Albumen  basic.     Histon  and  protamin. 

c.  Albumen  aromatized. — Melanins. 


CHAPTER  VII. 

ENZYMES. 

A  WORK  on  physiological  chemistry  no  matter  how  elemen- 
tary cannot  be  considered  complete  at  the  present  time  without 
a  few  words  on  the  subject  of  Enzymes. 

Enzymes  are  soluble  unorganized  ferments  secreted  by  cells, 
both  animal  and  vegetable ;  their  main  object  being  so  to  pre- 
pare the  food  for  the  cells  that  the  latter  can  readily  assimilate 
it.  The  action  occurs  quite  independently  of  the  life  of  the 
secreting  cell :  it  is  not  a  vital  process. 

Until  recently  a  distinction  was  always  made  between  organ- 
ized and  unorganized  ferments ;  the  latter  being  the  enzymes 
under  consideration,  and  the  former  various  micro-organisms 
—  bacteria,  yeasts  and  moulds  —  which  were  supposed  to 
exert  their  ferment  action  solely  by  means  of  vital  proc- 
esses. This,  however,  is  a  distinction  without  a  difference, 
since  it  is  now  known  for  certain  that  micro-organisms  also 
effect  ferment  actions  by  means  of  soluble  enzymes  which  they 
secrete  just  as  is  the  case  with  cells  of  the  higher  animals  and 
plants. 

The  term  "  vital  process "  may  be  objected  to  as  being 
merely  a  cloak  to  cover  our  ignorance.  That  is  precisely  what 
it  is.  We  can  follow  up  the  processes  which  go  on  in  indi- 
vidual cells  or  the  body  as  a  whole,  and  explain  them  as  due  to 
purely  chemical  or  physical  reactions  up  to  a  certain  point,  but 
beyond  this  we  know  practically  nothing. 

Our  knowledge  of  what  is  meant  by  life  is  a  little  more  ex- 
tensive than  it  was,  but  even  yet  is  a  mere  nothing  by  compari- 

160 


ENZYMES.  161 

son  with  our  ignorance.     The  cloak  covers  a  little  less  than  it 
did,  but  it  is  the  same  old  cloak  still. 

It  has  hitherto  been  found  impossible  to  isolate  enzymes  and 
study  them  in  a  pure  condition,  so  that  their  constitution  is  un- 
known, and  it  is  even  uncertain  if  they  are  of  a  proteid  nature 
or  not,  but  their  functions  have  been  very  thoroughly  studied 
and  a  large  number  of  different  kinds  are  known. 

1.  Enzymes  are  catalyzers. 

An  astonishingly  small  amount  of  an  enzyme  can  apparently 
exert  its  action  upon  an  unlimited  amount  of  a  given  substance, 
and  emerge  with  undiminished  vigor.  It  is  not  used  up  during 
the  reaction. 

Again  the  enzymes  are  simply  accelerators  of  reactions  which 
would  ultimately  take  place  without  their  aid.  They  do  not 
originate  the  reaction  in  which  they  are  concerned  (p.  10). 

2.  The  action  of  enzymes  is  specific. 

A  given  enzyme  will  act  on  a  given  substance  or  group  of 
closely  allied  substances,  and  on  no  other.  This  rule  however 
is  not  universal ;  several  exceptions  are  known. 

SUSCEPTIBILITY. 

Enzymes  are  very  susceptible  to  certain  external  influences. 
Heat  above  65°  C.  to  70°  C.  and  certain  poisons  will  destroy 
them,  although  some  substances  which  are  poisonous  for  a  cell 
are  not  so  for  its  enzymes. 

Chloroform,  thymol,  toluol  for  instance  will  destroy  the  life 
of  a  cell  but  have  little  or  no  effect  on  enzymes.  Mercuric 
chloride  is  a  poison  for  both. 

Chloroform  or  thymol  are  often  added  to  a  solution  in  which 
the  action  of  enzymes  is  being  studied.    They  prevent  bacterial 
growth  which  might  vitiate  the  results,  but  do  not  affect  the 
enzymes. 
11 


162         OUTLINES  OF  PHYSIOLOGICAL  CHEMISTRY. 

NOMENCLATURE. 

The  suffix  "  ase  "  is  given  to  an  enzyme  and  this  is  preceded 
by  the  name,  or  its  root,  of  the  substance  upon  which  it  acts. 
Thus  the  enzyme  which  acts  upon  Maltose  is  called  Maltase. 

This  momenclature,  however,  has  not  yet  been  universally 
adopted  and  it  is  not  possible  to  use  it  in  every  instance. 

ZYMOGENS  OR  PROFERMENTS. 

Enzymes,  more  particularly  those  of  the  digestive  tract  in 
animals,  often  exist  in  the  cells  in  an  inert  form,  and  only  be- 
come active  at  the  moment  of  their  discharge  from  the  cell.  In 
this  form  they  are  called  zymogens  or  pro-enzymes.  Zymogens 
may  develop  into  the  active  state  even  after  the  death  of  the 
cell  which  contains  them. 

If  a  pancreas,  for  example,  is  minced  fine  immediately  after 
death  and  the  juices  pressed  out,  the  extract  will  digest  fibrin 
and  other  proteids  very  slightly,  but  after  keeping  the  pancreas 
for  some  days  aseptically  extracts  from  it  will  digest  fibrin  very 
readily.  The  digestive  enzyme  was  present  in  the  first  instance 
as  trypsinogen,  which  on  keeping  changes  to  the  active  trypsin. 

The  enzymes  secreted  by  animals,  plants  and  the  lower  in- 
termediate forms  of  life,  are  in  the  main  similar,  although  there 
are  some  substances  peculiar  to  plants,  such  as  glucosides,  which 
are  acted  upon  by  plant  enzymes  alone. 

It  is  naturally  the  animal  enzymes  which  most  interest  us. 

Having  thus  given  briefly  a  few  points,  some  of  which  will 
be  discussed  more  in  detail  as  occasion  arises,  about  enzymes 
as  a  whole,  we  may  proceed  to  classify  them  according  to  their 
functions. 

1.  The  hydrolyzing  enzymes,  which  may  be  called  Hydrases. 

2.  The  coagulating  (clotting)  enzymes,  which  may  be  called 
Coagulases. 


ENZYMES.  163 

3.  The  oxidizing  enzymes,  which  may  be  called  Oxidases. 
Another  classification  may  be  made. 

1.  Those  which  act  extracellularly,  i.  e.,  are  diffused  out  of 
e  cell  to  do  their  work,  into  the  intestinal  canal,  for  instance. 

2.  Those  which  act  intracellularly,  i.  e.,  are  retained  within 
cell  and  work  there. 

These  two  groups,  however,  are  alike  in  their  action,  i.  e.y  an 
zyme  acting  on  starch  or  glycogen  will  affect  it  in  precisely 
the  same  way  whether  it  is  an  extra  or  intracellular  one,  so  that 
the  difference  is  only  one  of  location.  We  will,  therefore,  dis- 
cuss the  individual  enzymes  according  to  the  former  grouping. 

I.  THE  HYDKOLYZING  ENZYMES  OR  HYDBASES. 
The  substances  of  most  interest  to  us  which  can  be  hydro- 
lyzed  by  enzymes  are  carbohydrates,  fats  and  proteids. 

§A.  Enzymes  Hydrolyzing  Carbohydrates. 
1.  Enzyme  hydrolzing  starch  (Polysaceharide). 
Amylase  (amylum  starch)  splits  the  complex  starch  molecule 
into  maltose ;  a  disaccharide,  with  dextrin  as  an  intermediate 
product.     Starch  as  it  occurs  in  seeds,  roots,  etc.,  is  insoluble 
and  the  first  action  of  the  enzyme  is  to  split  up  the  highly  com- 
plex insoluble  starch  molecule  into  a  less  complex  form  of 
starch  which  is  soluble.     The  soluble  starch  is  then  simplified 
to  dextrins  and  these  in  turn  to  maltose. 

But  it  is  probable  that  during  the  whole  process  maltose  is 
being  continually  split  off  as  such,  so  that  the  process  may  be 
put  diagrammatically  as  : 

12  monosaccharides.  10  monosaccharides. 


Starch  (insol.)  =  Maltose  +  Soluble  starch. 

+  I  II  I  +  I 


Soluble  Starch.  Maltose.  Dextrin.  Dextrin. 

and  the  dextrin  then  hydrolyzed  to  maltose. 


164  OUTLINES   OF    PHYSIOLOGICAL    CHEMISTRY. 

The  reserve  material  stored  up  in  seeds  and  bulbs  consists 
principally  of  starch,  and  as  these  begin  to  grow  the  starch  is 
converted  by  amylase  secreted  in  special  cells  into  maltose  in 
which  form  it  can  be  utilized  by  the  newly  forming  sprouts. 

Vegetables  taken  as  food  by  animals  contain  large  quantities 
of  starch  which  is  attacked  by  the  extracellular  amylase  of  the 
saliva  (ptyalin)  and  pancreas  (amylopsin)  and  so  converted  into 
the  soluble  disaccharide  maltose. 

Glycogen  or  animal  starch  is  stored  up  in  the  liver  and  can 
also  be  hydrolyzed  to  maltose  by  amylase.  Amylase  is  present 
in  the  liver  cells  and  here  acts  as  an  intracellular  enzyme. 

2.  Enzymes  Hydrolyzing  Disaccharides. 

Disaccharides  cannot  be  assimilated  as  such,  but  must  be 
first  hydrolyzed  to  monosaccharides.  This  is  effected  by  means 
of  enzymes  of  which  the  principal  are  : 

(a)  Saccharase  hydrolyzes  saccharose  to  glucose  +  fructose. 

(Invertase.)  (Cane  sugar.)  (Invert  sugar.) 

(6)  Maltose  hydrolyzes  maltose  to  glucose  -f  glucose. 
(c)  Lactose          "          lactose  to  glucose  +  galactose. 

(Milk  sugar.) 

(a)  Saccharase  or  invertase  is  secreted  by  the  cells  of  the 
small  intestine  and  the  products  of  its  action  on  saccharose — 
glucose  and  fructose  can  then  be  absorbed  and  assimilated. 

(b)  Maltose  is  also  secreted  in  the  small  intestine,  where  it 
splits  up  the  maltose  already  prepared  by  amylase  (ptyalin  and 
amylopsin)  into  two  molecules  of  glucose.     Maltase  also  prob- 
ably exists  in  the  blood,  since  maltose  which  finds  its  way  there 
in  small  amounts  is  changed  to  glucose.     Large  amounts  of 
maltose  introduced  into  the  circulation  appear   in  the  urine 
unchanged. 

(c)  Lactose  is  apparently  not  secreted   in  the  intestine  or 
elsewhere  in  the  body,  but  a  great  deal  of  lactose  is  taken  in 
by  sucklings  with  the  mother's  milk.     It  seems  probable  that 


ENZYMES.  165 

the  lactose  contained  in  milk  is  split  up  in  the  intestine  by 
bacteria  and  thus  becomes  available  for  assimilation. 

The  Bacillus  coli  communis,  which  is  a  normal  inhabitant  of 
the  large  intestine,  secretes  lactase :  Many  varieties  of  coli 
communis  also  secrete  saccharase  and  it  is  possible  that  a  part 
of  the  saccharose  ingested  is  rendered  available  by  this  means. 

B.  Enzymes  Hydrolyzing  Fats. 

Lipase  (XtVo?  fat)  is  secreted  by  the  pancreas  (steapsin)  and 
is  discharged  into  the  duodenum,  where  it  splits  the  fats  into 
glycerin  and  a  fatty  acid. 

The  fats  are  emulsified  by  the  juices  in  the  intestine  and  be- 
ing thus  in  a  very  fine  state  of  division  are  easily  reached  by 
the  lipase. 

The  glycerin  is  absorbed  as  such,  and  the  fatty  acid,  combin- 
ing with  any  sodium  or  potassium  present,  forms  a  soluble  soap. 
It  is  in  the  double  form  of  glycerin  and  a  soluble  soap  that 
the  fats  reach  the  cells  ;  once  there  the  fat  is  built  up  again. 
Lipase  is  also  found  in  most  of  the  body  cells  as  an  intracellular 
enzyme. 

C.  Enzymes  Hydrolyzing  Proteids. 

Proteolytic  Enzymes  —  Proteases.  —  The  proteases  break  up 
the  complex  insoluble,  or  if  soluble  non-dialyzable,  proteid 
molecules  to  peptones  which  can  be  absorbed  by  the  intestinal 
cells,  and  to  some  extent  the  peptones  still  further  to  amino 
acids.  Pepsin,  secreted  in  the  stomach,  and  trypsin  in  the 
pancreas,  are  always  so  fully  treated  of  in  works  on  physiology 
that  they  need  not  be  discussed  here  in  detail. 

Two  additional  animal  proteolytic  enzymes  have  recently 
been  described.  Erepsin  and  Enterokinase. 

Erepsin  is  said  to  be  secreted  by  the  cells  of  the  small  in- 
testine, its  function  being  to  extend  the  action  of  trypsin,  tryp- 


166  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

sin  according  to  this  idea  being  unable  to  carry  digestion  farther 
than  peptones,  the  erepsin  then  hydrolyzing  the  peptones  to 
amino  acids. 

Enterokinase,  secreted  by  the  cells  of  the  intestine  is  said  to 
activate  trypsin,  the  latter  being  of  itself  quite  inert  at  the 
moment  of  passing  into  the  intestine. 

If  a  pancreatic  fistula  is  made  in  a  dog  the  juice  passing  out 
can  be  collected.  Such  juice  is  said  to  have  no  digestive  action 
on  fibrin  or  other  proteids,  but  it  is  at  once  activated  on  adding  a 
little  juice  from  the  small  intestine.  The  latter  is  said  to  con- 
tain the  activating  enterokinase.  It  may  be  that  the  trypsin  is 
present  in  the  form  of  a  soluble  zymogen.  Statements  about 
these  new  enzymes  however  must  still  be  accepted  with  some 
reserve. 

The  Clotting  Enzymes.     Coagulases. 

Rennet  which  clots  milk  and  the  fibrin  ferment  (thrombase) 
which  clots  blood,  like  pepsin  and  trypsin,  are  always  so  fully 
discussed  that  they  need  not  be  more  than  mentioned  here. 
The  presence  of  calcium  salts  seems  to  be  necessary  for  their 
action  and  it  is  thought  that  clotting  is  due  to  the  formation  of 
a  calcium  salt  of  the  casein  or  fibrin  as  the  case  may  be.  But 
this  is  still  uncertain ;  the  exact  way  in  which  the  coagulases 
act  is  not  known. 

Plasmase  is  a  recent  discovery.  It  is  secreted  in  the  stomach 
and  is  said  to  have  the  property  of  coagulating  albumen  and 
albumoses  which  are  then  digested  by  the  proteolytic  enzymes. 
But  this  requires  confirmation. 

Oxidizing  Enzymes.     Oxidases. 

It  has  always  been  a  puzzle  why  certain  substances  such  as 
albumen,  which  are  oxidized  with  great  difficulty  in  the  labo- 
ratory, can  be  easily  oxidized  in  the  body,  whilst  on  the  other 


ENZYMES.  167 

hand  certain  substances,  such  as  oxalic  acid,  easily  oxidized  by 
the  chemist,  pass  through  the  body  unchanged. 

Until  recently  it  was  necessary  to  put  these  oxidation 
processes  under  the  heading  of  "  vital  processes,"  but  the  exist- 
ence of  specific  oxidizing  enzymes  in  plants  is  now  proved  and 
it  has  been  sought  to  show  that  such  occur  also  in  animal 
tissues  :  specific  enzymes  which  will  oxidize  definite  substances 
but  allow  others  to  pass  by. 

The  oxidizing  enzymes  are  carriers  of  oxygen.  It  is  sup- 
posed that  they  yield  oxygen  to  the  substances  to  be  oxidized 
and  then  instantaneously  reoxidize  themselves.  In  this  they 
differ  from  oxidizing  substances  such  as  potassium  permanganate 
and  chromic  acid,  which,  once  deprived  of  their  O,  remain 
reduced  and  inert.  Some  Fe  and  Mn  oxides  and  salts,  how- 
ever, can  yield  O  and  then  reconstruct  themselves,  but  their 
action  is  slow  compared  with  the  oxidizing  enzymes  which 
work  with  inconceivable  rapidity. 

Oxidases  have  the  power  of  turning  guaiac  tincture  blue,  by 
oxidizing  it,  and  are  divided  into  two  main  groups  according 
to  the  differences  in  their  action  on  it. 

1.  Those  which  turn  guaiac  blue  direct,  utilizing  the  O  =  O 
of  the  air  for  their  reconstruction  :  Direct  Oxidases. 

2.  Those  which  do  not  turn  guaiac  blue  until  the  addition 
of  H2O2.     Indirect  or  Peroxidases. 

All  protoplasm  contains  an  enzyme,  Catalasey  which  has  the 
power  of  reducing  H2O2  to  H2O  and  O.     The  liberated  O  =  is 
then  used  by  the  peroxidases,  but  they  cannot  use  O  =  O  of 
the  air  to  reoxidize  themselves.     The  O  must  be  nascent. 
Briefly. 

\.  Direct  Oxidases  utilize  O  =  O. 

2.  Peroxidases  utilize  O  =  . 


168  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

Plants  contain  both  of  the  oxidases,  but  in  animal  tissues 
only  the  latter  are  present. 

Animal  peroxidases  are  never  poured  out  into  the  digestive 
tract ;  their  field  of  action  is  altogether  intracellular. 

Animal  tissues  then  will  liberate  O  =  from  H2O2  by  means 
of  their  catalase,  and  the  question  then  arises  :  "  Is  not  the 
oxidation  of  the  guaiac  due  simply  to  the  O  =  liberated  by 
catalytic  action  on  H2O2?"  That  it  is  not  so  oxidized  but 
requires  a  carrier  can  be  shown  by  means  of  bacterial  cul- 
tures. 

Take  an  agar  culture  of  any  common  bacillus  and  pour  into 
the  tube  2  or  3  c.c.  of  an  emulsion  of  gum  guaiac,  and  then  1 
or  2  c.c.  of  H2O2.  There  is  very  active  evolution  of  gas.  O= 
must  be  given  off  in  great  abundance,  yet  there  is  no  bluing 
of  the  guaiac.  In  10  or  15  minutes  add  a  little  blood.  A 
blue  color  immediately  appears. 

The  bacteria  contain  catalase  but  no  peroxidase. 

We  may  take  it  as  probable  then  that  catalase  and  peroxidase 
are  two  separate  enzymes ;  the  one  reducing  and  the  other 
transferring  the  O  =  to  other  substances. 

It  seems  legitimate  to  suppose  that  the  reduction  of  oxyhem- 
oglobin  (HBO)  in  the  body  is  due  to  the  catalase  which  thus 
becomes  the  medium  by  which  O  ==  is  supplied  to  the  tissues  ; 
the  peroxidase  acting  as  carrier  and  so  assisting  oxidation. 
But  we  must  be  very  careful  not  to  attach  much  importance  to 
peroxidase.  We  know  that  fats,  sugars  and  proteids  are  oxi- 
dized in  the  body,  and  we  know  that,  outside  the  body  at  any 
rate,  these  are  not  influenced  by  peroxidase  in  the  least.  All 
we  know  about  peroxidase  is  that  it  will  oxidize  guaiac,  but  we 
have  no  idea  what  else  it  can  do. 

It  has  been  claimed  that  apart  from  the  peroxidases  enzymes 
are  present  in  the  liver  and  some  other  organs,  which  even 


ENZYMES.  169 

after  death  will  oxidize  aldehydes  (e.  g.,  salicyl  aldehyde)  to 
acids.  These  have  been  called  aldehydases. 

But  aldehydes  are  so  greedy  for  oxygen  that  the  mere  pres- 
ence of  O=  is  sufficient  for  their  oxidation,  so  it  appears  super- 
fluous to  assume  a  special  oxidizing  enzyme  for  this.  O  =  lib- 
erated by  catalase  is  all  that  is  needed  for  oxidation  of  aldehydes. 

The  guaiac  test  for  oxidases  is  simple  and  may  be  briefly 
described. 

Put  some  lumps  of  gum  guaiac  into  a  test-tube  containing 
alcohol  and  boil  over  burner  until  deep  yellow.  Filter  and 
add  the  filtrate  to  water  in  a  test-tube  or  porcelain  dish  to  the 
point  of  a  milky  emulsion. 

1.  Into   this    put   a  slice   of  potato.     A   deep   blue   color 
quickly  appears  which  diffuses  around  the  slice.     Direct  ox- 
idases. 

2.  Instead  of  potato  put  in  some  blood  or  a  piece  of  animal 
tissue  minced  fine.     No  reaction. 

Add  a  little  H2O2  and  a  blue  color  quickly  appears.     Peroxi- 


This  is  a  classical  test  for  blood.  Even  if  the  blood  has  been 
dried  out  for  months  it  will  give  the  reaction. 

3.  Bubbles  appear  on  the  surface  of  the  tissue.     Catalase. 

The  H2O2  is  being  reduced  to  H2O  and  O. 

If  the  potato  or  animal  tissue  is  previously  boiled  no  reac- 
tion occurs.  Both  the  catalase  and  the  oxidases  have  been  de- 
stroyed. 

As  has  already  been  said,  of  the  peroxidases  we  know  prac- 
tically nothing  beyond  the  fact  that  they  exist,  but  of  the  direct 
plant  oxidases  there  are  several  different  kinds  which  afford 
various  definite  reactions,  but  the  classification  into  two  main 
groups  as  already  given  is  as  much  as  can  be  attempted  here. 


170  OUTLINES    OF    PHYSIOLOGICAL   CHEMISTRY. 

We  may  however  mention  tyrosinase. 

Certain  fungi  (Russula  and  Boletus),  if  cut  with  a  knife,  turn 
red  or  blue  and  finally  black  on  the  cut  surface.  The  coloring 
is  due  to  a  melanin  formed  by  the  action  of  a  direct  oxidizing 
enzyme,  tyrosinase  on  tyrosin.  Both  tyrosin  and  tyrosinase  ex- 
ist free  in  the  plant  but  only  come  in  contact  when  the  tissues 
are  injured. 

The  tyrosin  is  oxidized  by  the  enzyme,  and  the  oxidation 
products  condense  into  a  highly  complex  melanin.  Whether 
the  enzyme  causes  the  condensation  as  well  as  the  oxidation  is 
not  known. 

The  ink  of  the  squid  to  which  we  have  already  referred  is  a 
similar  substance  also  formed  by  tyrosinase,  and  it  may  be  that 
some  other  animal  pigments  are  produced  in  the  same  way,  but 
it  is  not  yet  known  if  this  is  the  case  or  not. 

Tyrosinase  extracted  from  russula  or  boletus  is  often  used  as 
a  test  for  tyrosin.  The  merest  trace  of  tyrosin  in  a  solution 
can  be  detected  in  this  way  by  darkening  of  the  fluid. 

REVERSING  ACTION  OF  ENZYMES. 

Referring  again  to  the  hydrolyzing  enzymes  we  found  that 
they  break  down  complex  into  simpler  substances  without  be- 
ing themselves  affected.  They  are  catalyzers.  But  although 
the  enzymes  are  not  used  up,  yet  they  are  never  able  entirely 
to  complete  the  change. 

Taking  maltase  as  an  example :  If  this  is  added  to  concen- 
trated, 20  per  cent.,  solution  of  maltose,  it  will  change  86  per 
cent,  into  glucose,  but  leave  14  per  cent,  unchanged.  The  per- 
centage varies  with  the  dilution.  In  a  dilute  solution  a  larger 
percentage  is  changed  but  there  is  always  some  maltose  left. 
It  was  formerly  thought  that  the  glucose  formed  acted  as  a  re- 
strainer  of  the  enzyme  action  but  this  is  not  the  case,  for  on 


ENZYMES.  171 

taking  a  solution  in  which  the  action  has  ceased,  and  adding 
more  maltose  the  action  begins  again,  although  there  is  just  as 
much  glucose  present  as  before,  and  this  renewed  action  does 
not  cease  until  a  definite  relation  is  attained  between  the  amount 
of  maltose  and  glucose. 

There  is  a  point  of  equilibrium  (p.  7)  beyond  which  the 
enzyme  is  unable  to  carry  the  action. 

Within  the  last  few  years  a  very  curious  fact  has  been  as- 
certained with  regard  to  maltase.  If  it  is  added  to  a  concen- 
trated, 40  per  cent,  solution  of  pure  glucose  it  reverses  its  action, 
and  starts  in  to  build  up  maltose.  It  will  do  this  until  the  nat- 
ural equilibrium  for  this  particular  concentration  is  reached,  i.  e.9 
14  per  cent,  of  maltose.  Then  the  action  stops.  There  is  com- 
plete analogy  with  purely  chemical  reactions.  Constant  break- 
ing down  of  maltose  but  constant  building  up  at  the  same  rate. 


Glucose 86£  14£  "Maltose 


E.    Point  of  equilibrium. 

Such  a  reversing  action  has  been  demonstrated  for  maltase 
and  lipase,  but  not  so  far  for  other  enzymes,  although  it  is 
quite  possible  they  may  have  the  same  power.  If  this  is 
proved  to  be  so  it  will  be  a  decided  step  in  advance,  since  it 
will  show  that  not  only  breaking  down  but  also  building  up 
can  be  carried  on  apart  from  the  actual  life  of  the  cell.  But 
there  are  still  innumerable  reactions  taking  place  in  the  cell  to 
account  for  which  no  enzymes  have  yet  been  discovered. 

We  are  for  instance  quite  ignorant  to  what  extent  the  per- 
oxidases  are  responsible  for  oxidation  processes.  Even  if 
enzymes  are  discovered  for  all  these  reactions  there  still  remains 
the  question  :  "  How  are  enzymes  formed  ?  " 


172  OUTLINES    OF   PHYSIOLOGICAL   CHEMISTRY. 

If  enzymes  are  constructive  as  well  as  destructive  the  ob- 
vious uses  of  the  intracellular  enzymes  are  enormously  extended. 
They  are  no  longer  mere  scavengers,  intended  to  break  down  and 
clear  away  what  is  no  longer  needed  by  the  cell,  but  are  the 
agents  by  which  the  cell  maintains  the  necessary  equilibrium 
between  its  protoplasmic  contents  and  those  of  the  surrounding 
medium,  i.  e.,  the  extracellular  blood  or  lymph  serum. 

PLANT  ENZYMES. 

Among  the  plants  all  the  enzymes  found  in  animal  tissue  are 
represented,  with  the  exception  of  the  fibrin  ferment  (Throm- 
base),  but  on  the  other  hand  there  are  a  number  of  enzymes 
peculiar  to  the  vegetable  kingdom. 

Among  the  more  important  are  : 

1.  Cytase  (cellulase),  which  hydrolyzes  cellulose  to  sugars. 

2.  Inulase,  which  hydrolyzes  inulin  (a  polysaccharide  allied 
to  starch)  to  sugar. 

3.  Glucosidases,  usually    called   glucoside    splitters,    which 
hydrolyze  glucosides  to  glucose  and  something  else  (p.  91). 

There  are  a  large  number  of  different  glucosides  in  plants  and 
a  large  number  of  different  enzymes  which  split  them.  One 
glucoside  and  its  enzyme  may  be  referred  to. 

Plant  indican  is  a  glucoside  and  the  enzyme  splitting  it  is 
called  indicase.  Its  action  is  as  follows  : 

/N 1  —0— glucose  -,  OH 

IN/ISJ  +H20  =          I       I    7I        +  glucose 

NH  NH 

Plant  indican.  Indoxyl. 

We  may  recall  urine  indican. 


Urine  indican.  Indoxyl. 


ENZYMES.  173 

The  indoxyl  in  each  case  then  oxidizes  itself  by  means  of 
Q  =  O  as  already  described  (p.  92)  to  indigo  blue. 

Indigo  is  obtained  by  crushing  the  leaves  of  the  indigo  plant. 
Indoxyl  is  liberated  by  the  indicase  and  changes  to  indigo  blue. 
The  chlorophyll  is  then  dissolved  out  of  the  leaves  by  alcohol 
in  which  indigo  blue  is  insoluble,  and  the  indigo  blue  then  dis- 
solved out  in  chloroform  to  separate  it  from  the  cellulose  skele- 
ton of  the  leaf. 

What  the  uses  of  glucosides  are  to  a  plant  are  somewhat 
obscure.  The  glucoside  and  its  enzyme  exist  side  by  side  in 
the  cell,  of  a  leaf  for  instance,  and  it  is  not  until  the  leaf  is 
bruised  or  dies  that  they  come  in  contact  and  the  reaction 
occurs.  Since  many  of  the  products  of  the  splitting  are  dis- 
agreeable to  the  taste  it  has  been  thought  that  these  may  serve 
as  a  warning  to  an  animal  which  is  eating  a  leaf,  not  to  eat 
another,  so  that  the  storing  up  of  the  glucoside  and  its  enzyme 
may  be  considered  as  a  protective  measure. 

But  in  some  cases  the  products  are  not  disagreeable,  to  our 
taste  at  least,  and  certainly  herbivorous  animals  will  eat  many 
glucoside-containing  leaves  with  apparent  satisfaction.  It  may 
be  that,  in  some  instances  at  any  rate,  this  is  a  convenient  way 
of  storing  glucose  so  that  it  is  ready  for  an  emergency.  The 
leaf  is  injured,  glucose  is  liberated  by  the  enzyme,  and  the  leaf 
uses  it  for  building  itself  up  again.  The  glucose  is  anchored 
to  a  cyclic  compound  to  preserve  it  in  stable  form  until  needed. 

AUTOLYSIS. 

If  a  piece  of  animal  tissue  or  organ  is  taken  from  the  body 
aseptically  and  kept  free  from  bacteria,  decomposition,  as  it  is 
ordinarily  understood,  does  not  take  place. 

If  such  aseptic  tissue  is  heated  up  to  70°  C.  or  80°  C.  for  an 
hour  or  so,  it  remains  unchanged  indefinitely,  but  otherwise  it 


174  OUTLINES   OF    PHYSIOLOGICAL   CHEMISTRY. 

undergoes  changes  which  are  not  those  of  decomposition  (bac- 
terial action)  but  analogous  to  the  digestive  processes  which  go 
on  in  the  intestinal  tract. 

It  is  gradually  digested  by  the  proteolytic  enzymes  contained 
in  the  cells.  Autodigestion  (Autolysis). 

The  products  are  the  same  in  both  instances,  albumoses,  pep- 
tones, and  amino  acids.  Hydrolysis  takes  place  but  no  oxida- 
tion. The  peroxidases,  by  means  of  which  oxidation  may  be 
partly  carried  on,  are  there,  but  are  powerless  to  act  because 
only  O  =  O  is  offered  them  instead  of  their  accustomed  O  = 
derived  from  HbO. 

The  cells  of  some  organs  also  contain  amylase  and  lipase,  so 
that  on  autolysis  the  glycogen  and  fats  if  present  are  hydrolyzed 
to  glucose  and  fatty  acids. 


CHAPTER  VIII. 

DISEASE  AND  IMMUNITY. 

ALTHOUGH  the  subjects  treated  of  in  this  chapter  belong  to 
pathology  rather  than  physiology  the  two  are  so  closely  allied 
jfchat  a  brief  sketch  may  be  attempted. 
In  a  general  way  we  may  say, 

Disease  is  caused  by  absorption  of  poison. 
Immunity  is  defense  against  poison. 
1.  Poisons  may  be  mineral  or  organic. 
The  organic  poisons  may  be  subdivided  into  : 

1.  Those  secreted  by  plants,  e.  g.,  \egetable  alkaloids. 

2.  Those  secreted  by  animals,  e.  g.,  snake  poisons. 

3.  Those  secreted  by  intermediate  forms  of  life,  e.  g.,  bac- 
terial poisons. 

4.  Waste  or  split  products  of  any  of  these  three  forms  of 
life,  which  may  or  may  not  be  poisonous.     These  may  be  called 
accidental  poisons. 

They  are  not  formed  by  the  organism  with  a  view  to  defense 
or  attack. 

PTOMAINS.     TOXINS.     LEUCOMAINS. 

It  is  necessary  to  have  a  clear  understanding  of  what  is  meant 
by  these  terms. 

A.  PTOMAINS. 

Bacteria  may  be  divided  into  two  groups ;  the  pathogenic, 
which  can  multiply  in  the  body  and  cause  disease,  and  the 
saprophytic,  which  are  not  able  to  multiply  in  the  living  body. 

Decomposition  of  flesh  is  due  to  saprophytic  bacteria  and  in 
the  process  they  split  up  the  proteid  matter  and  furnish  certain 

175 


176  OUTLINES   OF    PHYSIOLOGICAL   CHEMISTRY. 

soluble  basic  products,  chiefly  amins  and  oxyamins,  called 
Ptomains  (TTT^GL  corpse).  The  ptomains  are  not  necessarily 
poisonous  but  they  may  be  and  the  danger  of  eating  decompos- 
ing meat  or  fish  is  due  to  their  possible  presence.  The  ptomains 
belong  to  group  4. 

B.  TOXINS. 

Toxins  are  synthetic  products  of  bacteria. 

They  are  not  the  split  products  of  proteids  but  are  sub- 
stances synthesized  by  the  bacteria  inside  the  bacterial  cell. 
When  formed  they  may  diffuse  out  of  the  cell  or  be  retained 
within  it. 

As  an  example  of  each  case  we  may  take  the  bacilli  of 
diphtheria  and  typhoid. 

If  a  culture  of  diphtheria  bacilli  in  broth  is  grown  for  two 
or  three  weeks  and  then  filtered  through  a  porcelain  filter,  the 
filtrate,  although  free  from  bacteria,  is  poisonous.  It  contains 
a  soluble  toxin  excreted  by  the  bacilli. 

If  a  culture  of  typhoid  bacilli  in  broth  is  grown  for  two  or 
three  weeks  and  then  filtered  through  a  porcelain  filter,  the 
filtrate  is  harmless.  It  contains  no  toxin. 

But  if  the  bacilli  remaining  on  the  filter  are  dried,  thoroughly 
pulverized  and  suspended  in  water,  the  suspension  is  poisonous. 
The  bacterial  cells  contain  an  intracellular  toxin. 

The  courses  of  the  two  diseases  also  illustrate  this.  The 
diphtheria  bacillus  does  not  penetrate  the  tissues,  but  grows 
locally  and  superficially,  forming  a  membrane  on  the  surface 
of  the  throat  for  instance. 

But  from  this  point  its  soluble  toxins  are  absorbed  into  the 
system  and  cause  the  symptoms  of  the  disease.  Toxemia. 

Typhoid  is  a  slow  lingering  disease.  The  bacilli  get  into  the 
circulation  and  grow  there.  Period  of  invasion.  After  a  time 
some  begin  to  die  off  and,  the  bacteria  disintegrating,  the  intra- 


DISEASE    AND    IMMUNITY.  177 


cellular  toxins  are  liberated,  and  cause  the  fever.  Later  the 
bacilli  gradually  disappear  from  the  blood,  but  the  fever  con- 
tinues as  long  as  any  are  left.  Bacteremia  or  Septicemia. 

C.  LEUCOMAINS. 

Leucomains  are  the  products  of  the  splitting  of  proteid  by 
body  cells.  Leucomains  are  analogous  to  ptomains  and  may 
be  identical. 

For  instance  if  lecithin  is  acted  upon  by  bacteria,  cholin 
may  be  split  off.  Cholin  in  this  case  is  a  ptomain.  If  lecithin 
is  acted  upon  by  a  body  cell,  cholin  may  be  split  off.  Cholin 
in  this  case  is  a  leucomain. 

Leucomains  however  do  not  leave  the  body  as  such  in  health. 
They  undergo  oxidation  to  urea,  CO2  and  H2O.  But  in  certain 
pathological  conditions,  they  may  not  be  properly  oxidized,  and 
remaining  in  the  system,  act  as  poisons.  Autointoxication, 
uremia  for  instance. 

IMMUNITY. 

Immunity  is  the  resistance  of  the  body  to  poisons  and  its 
capability  of  ridding  itself  of  toxic  agents  such  as  bacteria. 

Immunity  may  be  natural  or  acquired. 

It  takes  a  certain  amount  of  any  given  poison  to  kill,  and 
the  smallest  amount  that  will  effect  this  is  usually  called  the 
minimum  lethal  dose,  M.L.D.  Supposing  a  rabbit  can  stand 
an  injection  of  .09  c.c.  of  diphtheria  toxin,  but  that  .1  c.c.  will 
kill  it,  .1  c.c.  is  the  M.L.D.  and  the  rabbit  has  a  natural  im- 
•  munity  against  .09  c.c. 

A  few  days  after  a  first  injection  of  .09  c.c.  into  a  rabbit  a 
second  dose  may  be  given,  and  it  now  takes  a  much  larger 
amount   to    kill;    perhaps  .2   c.c.     By    carefully   raising   the 
amounts  the  rabbit  will  soon  be  able  to  stand,  say  1.0  c.c.  or 
\  ten  times  the  M.L.D.,  without  being  affected. 
12 


178  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

To  its  natural  immunity  against  .09  c.c.  an  acquired  immunity 
against  .9  c.c.  has  been  added.  It  is  now  immune  to  1  c.c.  or  ten 
M.L.D.  and  is  said  to  have  been  immunized  to  diphtheria  toxin. 

Antitoxins.  —  If  some  of  the  serum  of  this  rabbit  is  injected 
into  a  second  rabbit  and  at  the  same  time  a  dose  of  diphtheria 
toxin,  greater,  even  considerably  greater,  than  the  M.L.D.  the 
second  rabbit  does  not  die. 

The  serum  of  the  first  rabbit  contains  something  —  Anti- 
toxin —  which  protects  the  second  rabbit. 

The  first  rabbit  has  been  actively  immunized  —  with  toxin. 
The  second  rabbit  has  been  passively  immunized  —  with  anti- 
toxin. 

This  is  the  basis  on  which  the  antitoxin  treatment  of  diph- 
theria has  been  built  up. 

Just  what  antitoxin  is,  is  still  a  matter  of  doubt,  but  since 
experiments  have  shown  that  toxin  can  be  neutralized  by  anti- 
toxin "  in  vitro,"  i.  e.,  in  test-tubes  in  the  laboratory,  the  neu- 
tralization clearly  cannot  be  due  to  "  vital  action."  Again  the 
antitoxin  is  used  up  in  the  process  so  it  is  not  a  catalyzer,  and 
its  action  is  not  analogous  to  that  of  enzymes. 

There  must,  therefore,  be  a  purely  chemical  combination  be- 
tween the  toxin  and  antitoxin,  and,  taking  this  for  granted, 
Ehrlich  has  constructed  a  theory  which,  for  the  present,  serves 
very  well  as  a  working  hypothesis. 

EHRLICH'S  THEORY  OF  ANTITOXINS. 
Every  cell  is  built  up  of  an  innumerable  number  of  proteid 
molecules,  which  can  be  divided  into  two  groups. 

1.  The  central  molecules,  which  are  concerned  in  cell  metab- 
olism. 

2.  The  peripheral  molecules,  which  are  concerned  in  cell  nu- 
trition. 


DISEASE   AXD    IMMUNITY. 


179 


DIAGRAM  L 


.  The  peripheral  molecules  are  built  up  of  a  large  number  of 
central  nuclei,  amino  acids,  etc.,  in  combination,  and  possess  in 
addition  side  chains  which  are  chemically  active.  We  may 
consider  benzoic  acid  C6H5.COOH  as  analogous,  the  COOH 
being  a  chemically  active  side  chain. 

By  means  of  their  side  chains  the  peripheral  molecules  are  able 
to  combine  with  side  chains  of  various  molecules  passing  along 
in  the  blood  current  and  anchor  them.  Analogy. — Benzoic  acid 
anchors  glycocoll  to  form  hippuric  acid.  Such  anchored  mole- 
cules may  be  passed  on  to  the  central  molecules  and  utilized 
by  them. 

A  toxin  molecule  is  anchored  in  the  same  way,  but  instead  of 
being  an  assistance  it  paralyzes  the  side 
chain  and  throws  it  out  of  action.  If 
many  of  the  side  chains  are  thus  thrown 
out  of  action  the  cell  dies,  and  if  a  suffi- 
cient number  of  cells  are  thrown  out 
of  action,  the  entire  organism  dies. 

The  toxin  has  killed  the  animal. 

But  the  amount  of  toxin  anchored 
may  only  be  sufficient  to  injure  the 
cell  temporarily,  so  that  it  can  recover. 
It  is  a  well-known  fact  that  injury  is 
followed  by  hypertrophy,  i.  e.,  over- 
production of  the  tissues  locally  at  the 
point  of  injury. 

For  Example.  —  A  callus  is  formed 
as  a  broken  leg  heals. 

Just    so    with    the    injured    cells. 
There  is  over-production  at  the  site  of 
injury,  i.   e.,  the   side  chains  of  the  A*>  Antitoxin  occupied  by  toxin. 
peripheral   molecules  (usually  called  cell   receptors).     These 


Mt  Molecules  of  cell ;  3/u  Mole- 
cules with  receptors ;  R,  Recep- 
tor; Jglf  Receptor  with  toxin  ;  T, 


180  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

may  be  produced  in  great  excess,  and  a  number  of  them  be- 
come detached  and  float  away  in  the  blood  current.  These 
cast-off  side  chains  or  receptors  are  the  antitoxins. 

They  have  now  acquired  specific  properties,  i.  e.,  will  an- 
chor the  particular  toxin  which  caused  their  production  but 
nothing  else. 

Additional  amounts  of  this  particular  toxin  now  introduced 
into  the  circulation,  do  not  reach  the  cells,  but  are  anchored 
and  rendered  inert  by  the  antitoxins  in  the  blood  current. 

The  cells,  therefore,  escape  injury.     (Diagram  1.) 

The  success  of  the  antitoxin  treatment  of  diphtheria  led  to 
hopes  being  entertained  that  all  bacterial  diseases  could  be 
equally  well  overcome  by  means  of  antitoxins. 

This,  however,  is  not  the  case.  Tetanus  and  diphtheria  kill 
by  toxemia  and  the  body  cells  form  antitoxins  to  resist  this,  but 
most  pathogenic  bacteria  cause  disease  and  death  by  bacteremia 
and  the  immunization  process  against  this  is  somewhat  differ- 
ent. Antitoxins  are  not  formed  in  bacteremia  or  only  to  a 
limited  extent ;  not  sufficient  for  the  blood  to  protect  other  ani- 
mals passively. 

IMMUNIZATION  AGAINST  BACTEREMIA. 
The  typhoid  bacillus  can  be  taken  again  as  an  example. 

AGGLUTININS. 

The  blood  serum  of  a  patient  with  typhoid  fever  acquires 
the  property  of  agglutinating  typhoid  bacilli.  Observed  in  a 
hanging  drop  under  the  microscope  the  bacilli  are  seen  to  be 
very  motile.  If  a  drop  of  diluted  normal  blood  serum  is  added, 
the  motility  is  not  affected,  but  on  adding  a  drop  of  diluted 
serum  of  a  typhoid  patient  the  bacilli  lose  their  motility,  and 
collect  together  in  clumps. 


DISEASE    AND    IMMUNITY. 


181 


The  clumping  can  also  be  observed  macroscopically  in  a 
test-tube.  If  to  1  c.c.  of  a  typhoid  culture  in  broth  1  c.c.  of 
typhoid  serum,  diluted  say  to  1-25  with  physiological  salt  solu- 
tion, is  added,  making  the  total  dilution  1-50,  the  mixture  soon 
appears  flaky,  small  clumps  become  visible  which  gradually  sink 
to  the  bottom  of  the  test-tube,  leaving  the  fluid  above  perfectly 
clear. 

This  is  called  the  clump  or  Widal  reaction  and  is  very  gen- 
erally employed  for  diagnosis  of  typhoid  fever. 

The  serum  of  rabbits  or  other  animals  inoculated  with  cul- 
tures of  typhoid  bacilli  also  acquires  agglutinating  properties. 
By  repeated  injections  the  serum  can  be  made  very  active,  so  that 
dilutions  of  1-20,000  or  even  higher  may  show  the  reaction. 

It  appears  that  under  the  in- 
fluence of  the  immune  serum  a 
sticky  substance  is  exuded  from 
the  bacilli.  This  is  called  the 
agglutinum  ;  and  the  active 
substance  in  the  serum,  the 
agglutinm. 

The  agglutination,  however, 
does  not  kill  the  bacilli.  It 
only  makes  them  somewhat 
inert,  so  that  in  the  presence 
of  agglutinins  they  cannot  mul- 
tiply or  only  very  slowly. 

Ehrlich's  theory  with  regard 
to  this  is  that  some  of  the  side 
chains  of  the  peripheral  mole- 
cules of  a  body  cell  are  sup- 
plied with  two  groups,  a  haptophore  (seizing),  and  a  toxophore 
(toxic)  group.  (Diagram  II.) 


DIAGRAM  II. 


AP 


o 


Bacillus 


H,  Molecules  of  cell ;  Mlt  Molecules  of 
Bacillus;  AP,  Agglutinophore  Group;  Ht 
Haptophore  Group ;  R,  Receptors  occupied 
by  agglutinins;  A,  Free  Agglutinin;  Alt 
Agglutinin  with  Receptor. 


182  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

The  haptophore  group  H  seizes  a  receptor  K  of  the  bacillus 
and  the  toxophore  or  agglutinophore  group  AP  influences  the 
bacillus  in  such  a  way  that  it  exudes  the  agglutinum. 

If  the  body  is  invaded  by  the  bacilli  so  many  of  these  parti- 
cular side  chains  are  thrown  out  of  action  that  the  cell  is  injured 
to  this  extent.  There  is  therefore  over-production,  and  many 
of  the  new  side  chains  are  cast  off  into  the  circulation  where 
they  occur  as  free  agglutinins.  The  agglutinins  are  specific. 
They  will  agglutinate  the  bacterium  of  invasion  but  no  other. 

PEECIPITINS. 

A  similar  curious  phenomenon  has  also  been  observed. 

If  a  broth  culture  of  typhoid  three  or  four  weeks  old  is 
filtered  through  porcelain  and  thus  freed  from  bacilli,  the  clear 
filtrate,  if  immune  serum  is  added,  will  shortly  become  flaky, 
with  formation  of  clumps  which  gradually  sink  to  the  bottom 
of  the  test-tube. 

This  is  the  precipitin  reaction.  The  active  substance  in  the 
serum  is  called  the  precipitin  and  the  passive  substance  in  the 
filtrate  which  is  precipitated  is  called  the  preeipitum. 

The  serum  in  this  case  must  be  much  more  concentrated  than 
for  agglutination.  A  serum  which  will  agglutinate  typhoid 
bacilli  in  dilution  of  1-10,000  will  probably  not  cause  precipi- 
tation in  a  filtrate  in  higher  dilutions  than  1-20  or  1-40. 

Filtrates  of  fresh  cultures  cannot  be  precipitated  in  this  way. 

The  preeipitum  is  probably  an  albumenous  substance  liberated 
on  the  death  of  the  bacilli,  and  is  no  doubt  closely  allied  to  the 
agglutinum  though  it  is  still  an  open  question  if  the  two  are 
identical  or  not. 

LYSINS. 

The  agglutinins,  as  already  mentioned,  do  not  kill  but  only 
hold  the  bacteria  in  check,  yet  the  bacteria  must  be  killed  in 
order  to  get  rid  of  them. 


DISEASE  AND   IMMUNITY.  183 

Normal  serum  if  fresh  will  kill  a  few  bacteria,  and  this  power 
is  greatly  increased  against  any  particular  bacterium  on  immuni- 
zation with  it.  This  increased  power  can  be  more  clearly 
demonstrated  "  in  vivo  "  than  "  in  vitro/'  by  means  of  what  is 
known  as  PfeifFer's  phenomenon.  Pfeiffer  experimented  with 
cholera  bacilli  but  the  same  thing  applies  to  typhoid. 

If  a  large  number  of  typhoid  bacilli  are  injected  into  the 
peritoneal  cavity  of  a  normal  guinea-pig  (or  rabbit,  etc.),  and  a 
small  quantity  of  the  peritoneal  fluid  withdrawn  from  time  to 
time  by  means  of  a  capillary  glass  tube,  microscopical  examina- 
tion shows  that  the  bacilli  after  two  or  three  hours  are  still 
numerous  and  actively  motile.  There  are  more  of  them  than 
the  normal  fluid  can  kill  and  in  all  probability  they  will  multiply 
and  set  up  a  fatal  bacteremia. 

If  the  same  thing  is  done  with  a  guinea-pig  immunized  to 
typhoid  the  bacilli  immediately  lose  their  motility  and  clump. 
Before  long  they  become  granular  and  begin  to  break  up.  Cul- 
tures taken  from  time  to  time  show  that  the  bacilli  are  killed 
within  a  few  hours.  The  agents  which  kill  them  are  called 
bacteriolysins. 

An  analogous  case  is  that  of  the  hemolysins,  i.  e.,  agents 
which  destroy  red  blood  corpuscles,  and  since  the  action  of  these 
is  much  more  easily  demonstrated  "  in  vitro  "  than  the  action 
of  bacteriolysins  it  is  chiefly  on  experiments  with  hemolysins 
that  Ehrlich  has  built  up  his  theory  of  the  lysins. 

We  can  take  two  animals,  the  goat  and  the  rabbit,  as  examples, 
but  what  applies  to  them  applies  to  other  animals  also. 

Normal  rabbit  serum  can  dissolve  the  red  corpuscles  of  a  goat 
to  a  very  limited  extent  in  a  test-tube,  but  this  power  is  enhanced 
to  a  remarkable  degree  if  the  rabbit  is  treated  with  successive 
injections  of  goat's  blood.  The  serum  of  the  rabbit  has  become 
strongly  hemolytic  for  goat's  corpuscles. 


184  OUTLINES   OF   PHYSIOLOGICAL,   CHEMISTRY. 

As  an  example  of  an  experiment  we  may  dilute  1  c.c.  of 
hemolytic  serum  with  99  c.c.  physiological  salt  solution  ;  take 
1  c.c.  of  the  dilution  in  a  test-tube  and  into  this  put  one  drop 
of  defibrinated  goat's  blood.  As  the  red  corpuscles  dissolve 
the  hemoglobin  diffuses  out  and  the  fluid  becomes  red.  To  see 
if  there  has  been  total  hemolysis  or  not  a  microscopical  exami- 
nation can  be  made. 

If  such  hemolytic  serum  is  warmed  to  60°  C.  for  30  minutes 
it  will  no  longer  destroy  goat  corpuscles.  It  has  become 
inactivated. 

Supposing  we  now  take  normal  rabbit  serum  and  add  a  few 
drops  of  it  to  the  fluid.  The  red  cells  are  quickly  dissolved. 
The  inactivated  serum  has  been  reactivated  by  normal  serum. 
Why  does  normal  serum  have  this  power?  We  shall  see 
directly. 

With  bacteriolysins  there  is  no  simple  method  of  observa- 
tion like  this,  as  bacteria  have  to  be  added  to  the  serum,  a 
loopful  of  the  fluid  plated  out  at  intervals  and  the  colonies 
counted  ;  a  tedious  and  not  very  accurate  method. 

But  the  bacteriolysins  act  in  just  the  same  way  as  hemolysins, 
so  we  can  now  return  to  our  typhoid  bacilli  to  work  out  the 
meaning  of  these  phenomena. 

Ehrlich's  theory  extended  to  the  lysins,  supposes  that  some 
of  the  peripheral  molecules  of  the  body  cells  contain  side  chains 
specially  constructed  to  grapple  with  bacteria,  and  probably 
other  inert  foreign  bodies  and  destroy  them.  It  must  be 
remembered  that  the  bacteria  themselves  appear  to  the  body 
cell  simply  as  inert  foreign  substances.  It  is  only  their  toxins 
which  actually  cause  direct  injury. 

Such  special  side  chains  contain  two  groups,  a  chemically 
active  haptophore  group,  and  a  latent  receptor  group. 

The  haptophore  group  can  seize  a  receptor  of  a  bacillus  and 


DISEASE    AND    IMMUNITY. 


185 


anchor  it,  but  cannot  of  itself  exert  any  influence  on  the 
bacillus.  But  as  soon  as  it  has  anchored  the  bacillus  its  latent 
receptor  group  becomes  chemically  active  and  capable  of 
receiving  a  body  which  is  normally  present  in  the  blood  called 
a  complement  (also  called  alexine  or  addiment). 

The  combined  action  of  the  complement  and  special  side 
chain  can  destroy  the  bacillus. 

But  although  the  cell  is  not  directly  injured  these  special  side 
chains  are  thrown  out  of  action, 
and  consequently  overproduc- 
tion takes  place :  Many  are  cast 
off  and  circulate  free  in  the 
blood  current.  They  are  now 
known  as  "  immune  "  or  "  inter- 
mediate9' bodies  or  ambocep- 
tors,  and  with  the  aid  of  the  com- 
plements destroy  the  bacilli. 

The  intermediate  bodies  like 
the  antitoxins  and  agglutinins 
are  produced  in  excess  in  im- 
munization, but  the  comple- 
ments do  not  increase  in  num- 
ber. They  exist  normally  in 
the  body  and  the  cells,  —  i.  e., 
the  leucocytes, — which  produce 
them  are  not  in  any  way  affected 
by  the  bacteria  so  there  is  no  tendency  to  over-production. 

Complements  are  destroyed  by  heating  to  60° C.  and  are  said 
to  be  thermolabile,  whilst  the  intermediate  bodies  are  only 
affected  at  considerably  higher  temperatures,  70-7 5 °C.,  so  are 
called  thermostable. 

We  can  now  understand  why  immune  serum  is  inactivated 


Bacillus 


M,  Molecules  of  cell ;  Mlt  Molecules  of  ba- 
cillus ;  It,  Receptors :  H,  Haptophore  Group; 
J,  Free  intermediate  body  ;  J,,  With  com- 
plement and  receptor  ;  C,  Free  complement ; 
Clt  With  receptor ;  (72,  With  intermediate 
body. 


186  OUTLINES    OF    PHYSIOLOGICAL   CHEMISTRY. 

by  heating  to  60 °C.  (Complements  are  destroyed,  but  not 
intermediate  bodies),  and  can  be  reactivated  by  adding  normal 
serum.  (Intermediate  bodies  supplied  with  fresh  complements.) 

Again  complements  once  separated  from  the  body  quickly 
break  up  and  disappear  from  the  serum,  whereas  intermediate 
bodies  remain  intact  for  months.  For  this  reason  serum  used 
in  experiments  with  lysins  must  be  fresh,  not  more  than  one 
or  two  days  old.  But  as  with  heated  serum  old  inactive 
immune  serum  can  be  reactivated  with  fresh  normal  serum. 
Pfeiffer's  phenomenon  does  not  show  with  a  normal  animal 
because  there  are  only  complements  present  in  the  peritoneal 
fluid,  whilst  with  an  immunized  animal  both  bodies  exist  free 
in  the  peritoneal  cavity. 

The  intermediate  bodies  are  specific.  They  will  only  attack 
the  particular  species  of  bacterium  or  blood  cell  against  which 
the  animal  has  been  immunized,  whilst  the  complements  are 
general,  being  able  to  combine  with  any  intermediate  body, 
although  it  may  be  that  bacterial  complements  are  not  the  same 
as  hemolytic  complements. 

It  must  be  confessed  that  this  has  been  put  in  a  very  general 
way.  There  are  numerous  partial  exceptions  to  the  rules  here 
laid  down  and  numbers  of  cases  which  do  not  seem  to  conform 
to  them  at  all.  The  consequence  of  this  is  that  Ehrlich  has 
been  obliged  so  to  extend  and  complicate  his  theory  to  meet  all 
the  requirements,  that  it  is  becoming  doubtful  if  it  will  stand 
the  strain  much  longer.  Some  new  and  more  simple  theory  for 
the  phenomena  of  bacteremia  is  urgently  needed  but  as  yet 
there  is  none  in  sight,  and  for  the  present  we  must  make  the 
best  we  can  of  Ehrlich's. 

A  study  of  the  reactions  against  bacteremia  and  the  theories 
to  account  for  them  makes  one  curious  to  know  what  is  the 
meaning  of  the  double  and  apparently  independent  action  of  the 


DISEASE  AND   IMMUNITY.  187 

agglutinins  and  bacteriolysins.  We  can  only  guess,  but  it  seems 
quite  possible  that  agglutination  is  a  means  of  holding  the  bac- 
teria in  check  until  they  can  be  destroyed. 

On  introducing  bacteria  into  the  circulation  some  are  at  once 
destroyed  by  the  cell  side  chains  and  complements,  and  as  soon 
as  intermediate  bodies  are  formed  still  more  can  be  destroyed. 
But  the  complements  are  soon  used  up  and  it  is  necessary  to 
wait  for  a  fresh  supply.  Meanwhile  side  by  side  with  the  inter- 
mediate bodies  free  agglutinins  have  been  produced  and  these 
help  to  prevent  multiplication  until  more  complements  are 
ready. 

The  question  then  arises  :  "  Why  is  not  some  provision  made 
for  a  larger  supply  of  complements  so  that  the  bacteria  may  be 
destroyed  more  quickly  ?  "  The  answer  seems  to  -be,  that  it 
would  not  do  to  kill  the  bacteria  off  too  quickly.  It  must  be 
remembered  that  they  contain  intracellular  toxins  which  are 
only  set  free  on  the  death  of  the  bacilli  and  against  these  in- 
tracellular toxins  antitoxins  do  not  appear  to  be  formed  or  at 
any  rate  only  to  a  limited  extent,  so  that  the  liberation  of  large 
amounts  of  toxins  all  at  once  would  be  dangerous  and  liable  to 
cause  the  death  of  the  organism. 

True  in  Pfeiffer's  phenomenon  a  large  number  of  bacteria  can 
certainly  be  killed  in  a  short  time,  yet  there  is  always  a  limit  to 
the  number,  depending  on  the  number  of  complements  present. 
We  are  dealing  here  too  with  highly  immunized  animals  which 
can  no  doubt  stand  a  large  dose  of  toxin  even  though  there  may 
be  little  or  no  antitoxin  in  the  blood. 

It  is  quite  possible  that,  instead  of  the  organism  as  a  whole 
becoming  immunized  to  the  intracellular  toxin  by  means  of 
antitoxin  in  the  circulation,  the  individual  cells  gradually  get 
hardened  to  it. 

Analogous  cases  can  be  found  in  mineral  poisons.    An  arsenic 


(88  OUTLINES   OF    PHYSIOLOGICAL   CHEMISTRY. 

eater  can  take  enough  arsenic  in  24  hours  to  kill  a  dozen  ordi- 
nary people,  yet  there  are  no  antiarsenic  bodies  in  his  blood. 
One  can  only  suppose  that  the  individual  cells  have  accustomed 
themselves  to  the  poison  in  some  way,  so  that  they  are  no  longer 
injured. 

It  may  be  said  that  no  antibodies  have  ever  been  experi- 
mentally produced  in  serums  against  poisons  of  a  relatively 
simple  nature  whose  chemical  constitutions  are  known. 

In  order  to  avoid  misunderstanding  it  may  be  mentioned  that 
a  number  of  workers  claim  to  have  succeeded  in  obtaining  anti- 
typhoid serums,  the  use  of  which  is  beneficial  in  cases  of  typhoid 
fever.  But  these  serums  have  never  come  into  general  use  and 
the  tendency  is  to  discredit  them.  The  same  may  be  said  of 
antistreptococcus  and  antipneumococcus  serums. 

On  the  other  hand  recent  experiments  by  Yaughan  indicate 
that  the  toxins  of  typhoid  and  intracellular  toxins  in  general 
are  relatively  simple  bodies,  against  which  one  would  not  ex- 
pect antitoxins  to  be  raised. 

By  breaking  down  the  bacterial  cells  with  sulphuric  acid  he 
has  extracted  virulent  toxins  which  resist  boiling.  Highly 
complex  molecules  would  certainly  be  destroyed  under  these 
conditions. 

Before  closing  the  chapter  a  further  reference  to  the  pre- 
cipitins  must  be  made. 

It  appears  that  any  albumenous  substance  when  injected  into 
an  animal  gives  rise  to  precipitins  in  the  serum,  i.  e.,  "anti- 
bodies "  which  will  precipitate  it  from  solution,  and  moreover 
the  anti-body  is  always  specific  for  that  particular  albumen. 
In  this  way  a  large  number  of  albumens  which  had  always  been 
supposed  to  be  precisely  alike  have  been  shown  to  differ  to 
some  infinitesimal  extent,  a  difference  which  cannot  be  detected 
by  their  ordinary  chemical  or  physical  (e.  g.,  salting  out)  re- 
actions. 


DISEASE  AND   IMMUNITY.  189 

Differentiation  of  albumens  by  this  means  is  called  the  bio- 
logical test. 

Examples:  1.  If  the  milk  of  a  cow  is  injected  into  a  rabbit, 
the  serum  of  the  latter  will  precipitate  the  casein  of  cow's 
milk,  but  not  that  of  human  or  other  milk,  or  only  to  a  very 
slight  extent. 

2.  If  the  blood  of  a  cow  or  ox  (beef  blood)  is  injected  into  a 
rabbit  the  serum  of  the  latter  will  not  only  contain  hemolysins 
but  also  precipitins,  so  that  on  adding  a  few  drops  of  the 
immune  rabbit  serum  to  1  c.c.  clear  beef  serum,  the  latter 
becomes  flaky  with  precipitation  of  clumps  to  the  bottom  of  the 
test-tube. 

This  reaction  is  made  use  of  as  a  test  for  human  blood. 

The  serum  of  a  rabbit  immunized  to  human  blood  (human- 
ized rabbit)  will  cause  a  precipitate  in  diluted  human  serum  or 
even  in  an  aqueous  solution  of  blood  which  has  been  dried  out 
for  months,  so  that  by  this  means  it  can  be  determined  if  blood 
stains  are  those  of  an  animal  or  human  being. 

The  precipitin  is  specific  though  not  absolutely  so.  A 
humanized  serum  which  will  precipitate  human  serum  at  1-100 
may  precipitate  that  of  an  ape  at  1-30,  and  that  of  a  dog  at 
1-10  for  example. 

The  more  nearly  related  the  animal  the  more  likely  is  its 
blood  to  react.  There  is  probably  strict  specificity  for  the  par- 
ticular albumen,  but  other  kinds  of  blood  may  contain  small 
proportions  of  it. 

We  may  suppose  that  human  blood  contains  of  albumen  A 
50  per  cent,  and  of  B  50  per  cent.,  both  of  which  give  rise  to 
precipitins.  The  blood  of  an  ape  may  have  10  per  cent,  of  A, 
20  per  cent,  of  B  and  70  per  cent,  of  C,  whilst  that  of  a  dog 
has  10  per  cent,  of  A,  10  per  cent,  of  C  and  80  per  cent,  of  D. 

If  three  rabbits  are  immunized,  each  with  one  kind  of  blood 


190  OUTLINES   OF   PHYSIOLOGICAL   CHEMISTRY. 

to  such  an  extent  that  the  serum  of  each  reacts  at  1-100  with 
its  blood  of  immunization  we  would  have : 

Human  Serum.  Ape  Serum.  Dog  Serum. 

Kabbit  No.  1  with  human  blood  1-100  1-30  1-10 

"       "    2     "    ape  "  1-30  1-100  1-20 

"       "    3     "    dog  1-10  1-20  1-100 

We  have  throughout  said  that  the  agglutinins  and  lysins  are 
specific,  but  they  are  not  absolutely  so  any  more  than  the  pre- 
cipitins.  It  has  therefore  been  suggested  that  all  these  reac- 
tions should  be  called  special  rather  than  specific,  but  there 
seems  no  good  reason  for  this.  They  are  specific  enough  for 
all  practical  purposes  so  may  just  as  well  be  designated  as  such. 

Probably  all  anti-bodies,  not  only  precipitins,  but  also  lysins 
and  agglutinins  are  formed,  not  against  particular  cells,  but 
against  particular  albumens  contained  in  those  cells.  Thus  a 
rabbit  serum  which  will  agglutinate  the  typhoid  bacillus  1-20,000 
may  agglutinate  the  Bacillus  coli  communis  1-100  or  1-200. 

This  simply  means  that  Bacillus  coli  communis  contains  a 
small  proportion  of  the  albumens  which  go  to  make  up  the 
protoplasm  of  the  typhoid  bacillus, 


Immunity. 


Against  albumens.  Against  simpler  substances. 

Antibodies  formed  and  No  antibodies.     Probably 

exist  free  in  individual  cells  accus- 

serum.  torn  themselves  to  the  poisons. 

~| 

Against  toxic  Against  inert  albumens 

albumens.  acting  as  foreign  bodies. 


Antitoxins.  Agglutinins.         Precipitins.         Lysins. 


POSTSCRIPT. 


191 


POSTSCRIPT. 

While  this  book  was  going  through  the  press  a  new  formula 
for  tryptophan  was  suggested  by  Ellinger  which  explains  very 
well  the  relations  existing  between  this  substance  and  kynurenic 
acid. 


.  CHa— NH, 
/\ — CH— COOH 


CH 


Tryptophan.  Kynurenic  acid. 

When  tryptophan  is  fed  to  a  dog  kynurenic  acid  is  ex- 
creted. If  gelatin,  which  does  not  give  the  Adamkiewicz 
reaction  and  therefore  does  not  contain  the  tryptophan  group, 
is  fed  kynurenic  acid  is  not  formed.  The  new  formula  for 
tryptophan  is  probably  the  correct  one  but  it  does  not  affect 
the  comparison  made  between  the  products  of  tyrosin  and 
tryptophan  on  p.  128. 


INDEX. 


Acids,  30 

Adamkievicz  reaction,  94 
Agglutinins,  181 
Albumens,  100 
Albumen  acid,  132 

alkali,  132 
Albumoses,  136 
Alcohols,  26 
Aldehydes,  28 
Alkaloid  reagents,  117 
Alkaloids,  95 
Allotropism,  15 
Amid  N,  61 
Amids,  59 
Amino  acids,  64 

diacids,  69 
Amins,  62 
Amylase,  163 
Anhydrids,  38 
Antitoxins,  178 
Arginin,  121 

Asymmetrical  C  atom,  40 
Autointoxication,  177 
AutolysiS)  174 

B 

Bacteremia,  180 
Benzene  ring,  74 

excretion,  81 
Binary  compounds,  137 
Biological  test,  188 
Biuret,  60 
Butane,  24 


Cadaverin,  108 
Carbohydrates,  47 
Carbon  molecule,  35 
Carbonic  acid,  38 
Carbylamin,  63 
Casein,  152 
Catalase,  167 

13 


Catalysis,  10 
Cholesterin,  90 
Cholin,  71 
Chondroitin,  143 
Coagulases,  166 
Coagulation,  101 
Collagen,  139 
Colloidal  sol.,  11 
Complements,  185 
Cresols,  83 
Cystin,  131 

D 

Diacids,  39 
Diamino  acids,  70 
Diatomic  alcohols,  39 
Diffusion,  11 
Dioxybenzenes,  78 
Disaccharides,  50 
Dissociation,  1 

acids,  4 

bases,  4 
Double  rings,  90 


E 


Elastin,  140 
Enterpkinase,  166 
Equilibrium,  7 
Erepsin,  165 
Esters,  37 
Ethane,  24 
Ethers,  36 

F 

Fats,  44 

Fehling'ssol.,  33 
Formulas,  empirical,  16 

graphic,  18 
Furfurol,  91 

a 

Gelatin,  140 
Glucosides,  91 
Glycocoll,  65 
Glycoproteids,  141 

193 


194 


INDEX. 


Glycoflamin,  70 
Glycuronic  acid,  48 
Guaiac  test,  169 
Guanidin,  61 

H 

Hematin,  146 
Hematoporphyrin,  146 
Hemin,  146 
Hemoglobin,  144 
Hexon  bases,  123 
Hippuric  acid,  82 
Histon,  153 
Homologues,  25 
Hopkin's  reaction,  94 
Hydrocarbons,  24 
Hydrolysis,  52 
Hydroxylamin,  85 


Immunity,  177 
Indican  plant,  172 

urine,  92 
Indicanuria,  93 
Indigo  blue,  92 
Indol,  92 

Intermediate  bodies,  185 
Ions,  2 
Isomers,  25 

K 

Keratin,  140 
Ketones,  28 


Lactic  acid,  40 
Lecithin,  71 
Leucin,  65 
Leucomains,  177 
Lipase,  165 
Lysin,  122 
Lysins,  182 


M 


Melanins,  156 
Melanoidins,  156 
Mercaptans,  54 
Methane,  23 
Millon's  reaction,  77 
Molisch'  s  reaction,  90 
Monpsaccharides,  48 
Mucin,  141 
Mucoids,  142 
Mustard  oils,  63 


N 

Naphthalene,  90 
Nitrils,  56 
Nitrobenzene,  76 
Nitrosoindol,  94 
Nitroso-reaction,  68 
Nitrous  acid  action,  67 
Nucleic  acid,  147 
Nuclein,  147 
Nucleo-proteids,  147 


Oils,  46 
Ornithin,  70 
Osazones,  89 
Osmosis,  15 
Oxidases,  166 
Oxidation,  13 
Oxyacids,  40 
Oxybenzenes,  75 


Peptones,  136 
Peroxidases,  167 
Pfeiffer's  phenomenon,  183 
Phenol,  75  ^ 
Phenylalanin,  83 
Phenyl  hydrazin,  84 
Phenylisocyanate,  84 
Piria's  test,  125 
Polysaccharides,  50 
Precipitation,  101 
Precipitins,  182 
Propane,  24 
Protamins,  155 
Proteases,  165 
Proteids,  alkaloid  tests,  117 

bases,  123 

color  tests,  116 

construction,  110 

nitrogen,  117 
,       nuclei,  106,  107 

phosphorized,  152 

phosphorus  in,  153 

products  of  bacteria,  108 
body  cells,  109 
hydrolysis,  106 
oxidation,  108 

sulphur  in,  130 
Proteides,  141 
Proteoses,  133 


INDEX. 


195 


Ptomams,  175 
Purin  bases,  95 
Putrescin,  108 
Pyrimidin  bases,  98 


Quinone,  79 


Reactions,  3 
Reduction,  13 
Reversion,  7 

enzymes,  170 

S 

Salting  out,  101 
Salicylic  acid,  82 
Saponification,  52 
Serin,  132 
Skatol,  93 
Soaps,  45 
Substitution,  23 
Sulphur  compounds,  54 
Synalbumose,  136 


Tartaric  acid,  43 


Taurin,  132 
Toxaemia,  176 
Toxins,  176 
Triatomic  alcohol,  39 
Trioxybenzenes,  80 
Tryptophan,  93 
Tyrosin,  83 

condensation,  127 


Unsaturated  compounds,  34 
Urea,  60 

production,  97 
Uric  acid,  95 

production,  149 


Wax,  46 


Xanthin,  95 
Xanthoproteic  reaction,  78 


Zymogens,  162 


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15  1938 


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